Bofors 40mm AA Fire Control/Directors
Iberian
control directors for their small AA guns, like their 40mm Bofors or the
25mm Japanese guns. For example, all american battleships (North Carolina,
SoDak and Iowas classes) had directors installed for their 40mm batteries
late in the war. Now, I have several questions:
- In general, were several 40mm mounts linked to the same director, or there
was a director per mount?
- Was the 40mm mount remotedlly controlled by the director (via an hidraulic
system), or were the gunners manually following pointers?
- If the 40mm mount was remotedly controlled by the director, what was the
purpose of having gunners/sight setters sitting in the mount gun, instead of
only ammo-loading personell? Was it just a redundancy measure in case of
electrical/hydraulic failure (as in SoDak, in order to revert to manual
control)?
- This small calliber 40/20mm (Bofors and Oerlikons) guns had a sight
callibrated for different target speeds (concentrical circles, the inner
ones for slower targets) for the optimal range of the gun, used to lead the
target. How did the gunners estimated target speed? (Or did they just gave a
damn about target speed, and tried to hose the target down with tracer
fire?).
- Could anybody describe how did the general fire control for 40mm worked,
from detection of the targets to allocation of the mounts and target
tracking?
Thanks for your answers.
A Sibilant Iberian.
Dennis Novak
There was a manual director used on some vessels. IIRC, it consisted of a
reflex type sight on a pedestal, linked to the gun drives. It was manually
aimed, but controlled the mount more quickly than the pointer and trainer could
by hand.
One nearly killed a f(r)iend of mine.
He was on a Fletcher I believe, working in the tub with the mount supposedly
deactivated. Someone turned the director head 180 degrees, and then turned on
the power. The mount trained, mashing my friend against a ready ammunition
rack. He woke up three days later in the sick bay of a cruiser, with a crushed
chest. He was told that someone got a court martial over the incident.
As to why there is still a pointer and trainer, they're there for the same
reason they are on every powered mount. Redundancy.
-Dennis Novak
B F Lake
//- In general, were several 40mm mounts linked to the same director, or
there
was a director per mount//
Single 40, no director. Twins and quads , director. Don't know if 40
mounts ganged per director. Info that radar mounted 40 director could also
direct 5" in AA.
//- Was the 40mm mount remotedlly controlled by the director (via an
hidraulic
system), or were the gunners manually following pointers?//
Twins all-electric driven, quads electric-hydraulic driven both by remote
director control, when crew pointer and trainer hands off, or local crew
hands on not directed
//- If the 40mm mount was remotedly controlled by the director, what was
the
purpose of having gunners/sight setters sitting in the mount gun, instead
of
only ammo-loading personell? Was it just a redundancy measure in case of
electrical/hydraulic failure (as in SoDak, in order to revert to manual
Yes, also chance of director/ director crew being hit by splinters etc
//- This small calliber 40/20mm (Bofors and Oerlikons) guns had a sight
callibrated for different target speeds (concentrical circles, the inner
ones for slower targets) for the optimal range of the gun, used to lead the
target. How did the gunners estimated target speed? (Or did they just gave
a
damn about target speed, and tried to hose the target down with tracer
20mm had manual operation , local ring and peep sight, tracer ammo.
Also could be aimed by a complicated sight giving a mirror view and
containing a gyroscopic device to compensate for the roll, pitch, yaw, or
speed change of ship. 20 crew had a "range setter" who set range data into
the gyroscopic sight.
40 single had trainer and pointer ring-peep sights, 40 twin and quad had
the same for local.
The remote director in a separate tub from the mount's generated a lead
angle and the solution elevation and training bearing were transmitted to
the mount's power drive to follow the director automatically. Range input
from director's radar. In local- mount driven by handwheels or by
"joystick" control of hydraulic system
//- Could anybody describe how did the general fire control for 40mm
worked,
from detection of the targets to allocation of the mounts and target
More or less by range zone as plane approached, gets too close for 5"
inside 8,000 yds, then 40s best range at about 2,800 yds, 20s had no
effective range as bullet too small to stop plane.
The gap from 3-8K yds was not filled in WW2, but was being worked on-the
3"/50 .
The 40 had a firing motor operated from the director in remote director
control. for local control, the pointer had a foot treadle firing and
also could work the firing motor by a clutch
An officer was the AA director, different guy from surface gunnery god. AA
officer assigned guns to targets (Think he worked in "Sky One" if my USN
argot correct)
//Thanks for your answers//
Thank T Roscoe, "US DD Ops WW2".
//A Sibilant Iberian.//
Good thing this is print medium. A sibilant Iberian attempting
aristocratic lithp -can't be done! Perhaps Portugesssssse ?<G>
Regards,
Barry
Iberian
here:
> 20 crew had a "range setter" who set range data into
> the gyroscopic sight.
Who gave this range to the 20mm crews (for their "range setter")? Was it
just a broad local estimation? I guess they were not linked through
headphones from the CIC (where they could give them a radar range), and even
if they were, how could they deconflict the target in a multiple aircraft
attack?
> The remote director in a separate tub from the mount's generated a lead
> angle and the solution elevation and training bearing were transmitted to
> the mount's power drive to follow the director automatically. Range input
> from director's radar.
The little info I have on the subject specifies a Mk-51 fire control system
for the 40mm Bofors, linked to a Mk-14 sight on the Bofors mount. This
director did not have any radar associated (not until the end of the war),
in fact in a picture of the director present in Norman Friedman's Naval
Weapons 91/92, you can clearly see what looks like a small optical
telemeter. Now, my new question is: How fast can you range an aircraft with
an optical telemeter? Is the procedure fast enough to deal with fast flying
close proximity threats (remeber we are talking 40mm close-in weapons
systems)?
> An officer was the AA director, different guy from surface gunnery god.
AA
> officer assigned guns to targets (Think he worked in "Sky One" if my USN
> argot correct)
This is what I don't get. How did the AA officer deconflict mounts? Suppose
we have three or four low-flying aircraft, how did he avoid having all the
40mm mounts engaging the same target? How did they avoid having all the
director mounts engaging the same target? (BTW, what is "Sky One"?)
>A sibilant Iberian attempting
> aristocratic lithp -can't be done! Perhaps Portugesssssse ?<G>
Nope... Ssssspanissssssh. Muchasss Grrraciassssss, Brrrian :-)
The Sibilant Iberian.
B F Lake
//> 20 crew had a "range setter" who set range data into
> the gyroscopic sight.
Who gave this range to the 20mm crews (for their "range setter")? Was it
just a broad local estimation? I guess they were not linked through
headphones from the CIC (where they could give them a radar range), and
even
if they were, how could they deconflict the target in a multiple aircraft
The single 20 on a pedestal had a crew of 5: the gunner (aims and fires)
trunnion operator (adjusts trunnion height to correspond with gunner's
position) range setter (for gyro sight) and two loaders. If no gyro sight,
then crew is 4. That's from the text of ref book. The drawing shows 4,
where is one loader and another man as communications number (="talker" in
USN) The "trunnion" in the drawing is operated by a "column raising wheel"
at the top of the pedestal on the left below the gun. Assume the talker
got the range from the foretop director on the gunnery broadcast (a
telephone/speaker voice net from the director officer to the weapon
positions) and passed it to the range setter (maybe the talker WAS the
range setter and save one body) (5 guys on one little gun is ridiculous!
Imagine a ship with these guns every where, and the number of bunks you
would need)
Target assignment comes from the director so the locals don't have to
deconflict. If more than one plane in their field of fire, just shoot at
closest till gone then shift to next- it is not complicated
//> The remote director in a separate tub from the mount's generated a
lead
> angle and the solution elevation and training bearing were transmitted to
> the mount's power drive to follow the director automatically. Range
input
> from director's radar.
The little info I have on the subject specifies a Mk-51 fire control system
for the 40mm Bofors, linked to a Mk-14 sight on the Bofors mount. This
director did not have any radar associated (not until the end of the war),
in fact in a picture of the director present in Norman Friedman's Naval
Weapons 91/92, you can clearly see what looks like a small optical
telemeter. Now, my new question is: How fast can you range an aircraft with
an optical telemeter? Is the procedure fast enough to deal with fast flying
systems)//
Dennis Novak posted about the optical director. Now here's where we need
expert input. The RN/RCN wartime 1943 twin 40 had a radar on the mounting
(282 radar). In late 40's, the RCN ditched these and went with a
(different?) twin 40 and got quads instead of the quad pom-poms from the
war. The 40s (except singles) had a separate director near each gun (one
for each ). The idea was to keep the director aimer out of the smoke and
vibration of the gun. The director was very like a 20 on a pedestal except
it was a sight and the aimer sort of swung around on his feet and this
moved the gun by remote. There was a "black box" in the middle of this
thing. Now it sounds to me that the gyroscopic sight for the 20 previously
described was a lot like this thing and also the director Dennis Novak
described. Also, when the Brits gave the USN a 40 mounting in late 1940 to
copy, they also included its "predictor" which is a separate director that
produces a lead angle for the gun that is following the director by remote.
OK- lets assume this beast is basically the same thing, and that post -war
the RCN went to wartime USN set up and did not bother with radar range
anymore because the target was so close anyway. ( or did they get a
proximity fuse for the 40?) Anyway, the range just wasn't a big deal.
When the target got close enough to engage it was only 2 miles away and
closing at say 240 knots, which is 4 miles a minute, so that's 30 seconds
and he's passed overhead or worse Kamikazied. If there was a lead angle,
it meant he was going after somebody else, so that's their problem, so the
director was more to keep the elevation on target.
//> An officer was the AA director, different guy from surface gunnery god.
AA
> officer assigned guns to targets (Think he worked in "Sky One" if my USN
> argot correct)
This is what I don't get. How did the AA officer deconflict mounts? Suppose
we have three or four low-flying aircraft, how did he avoid having all the
40mm mounts engaging the same target? How did they avoid having all the
Easy, there are AA guns all around the ship so you divide up the guns into
sectors of responsibility, you have voice comms with all your guns and
directors and broadcast a commentary on the targets for your ship and lets
say a plane is ahead and another abeam and the ship turns ninety degrees,
you warn the beam guns that they will take over the target that was ahead,
and tell the stern guns to engage the one that was abeam. "Sky One" was a
1930's USN name for the AA officer's action station in the foretop. The RN
had the same idea, but called it something else. This position would have
a good view and lots of telephones and ship's broadcast mikes to the
speakers around the ship by the guns, and he would have lookouts there etc.
//Nope... Ssssspanissssssh. Muchasss Grrraciassssss, //
Dos cerveza , por favor
Barry
ken...@cix.compulink.co.uk
NoAd...@IamTiredOfJunkMail.com (Iberian) wrote:
> - In general, were several 40mm mounts linked to the same director,
> or there
> was a director per mount?
Here is an extract from an article I wrote for the Naval Gazette.
> The major problem was with dive and torpedo aircraft. The rate of
change on bearing and elevation was too great to allow conventional
systems to track them. Also the earlier guns were on manual mounts and
did not have the room for follow the pointer systems anyway. The first
answer was to use open sights and tracer. The foresight was usually a
cartwheel type with aim off rings to allow for speed corrections. The
accuracy was nothing to write home about but as a deterrent to
attacking aircraft it worked especially with guns firing self
detonating shells. The next step was to fit gyro sights which helped
compensate for deflection.
None of this helped in concentrating fire from several mounts so
with the general adoption of powered mounts off mount fire control was
adopted. This usually consisted of a sight coupled to some sort of
computer remotely controlling several mounts. This was an area in
which the US was clearly ahead. The standard US director for light AA
during most of the war was the Mark 51 this had two gyros one
measuring lateral and the other vertical rate. This relied on the fact
that the guns would be firing at short range. This was combined with
remotely controlled power operated gun mountings. This system was
improved by the introduction of radar as a range finder though there
were problems in making sure that the radar was tracking the same
target as the optical system.<
As you can see from that the guns were remotely controlled. However
no WW2 remote control system was trusted enough to do away with the on
mount crew.
Ken Young
ken...@cix.co.uk
Maternity is a matter of fact
Paternity is a matter of opinion
B F Lake
//snip good info//
Also note that remote powered guns need to have mountings that are powered
in the first place, not moved by handwheel. This means adding motors and
drives which weigh something. The RN "utility" DDs were short of space for
fuel and with that, had no weight reserve for add-ons. The later C class
groups of 1944-5 had their second torpedo tubes suppressed to compensate
for having power-worked guns .
(Somewhere, there should be a really explicit exposure of whatever people
were causing the really bad RN gun development and production in the
30's/40's! Inability to figure out how to elevate guns to make them dp,
not powered, etc etc- compares with US torpedo testing lab as a thing to
really hate )
The hit probability in direct fire in 3 dimensional AA was so low that
barrage fire was chosen . A note from Thomas Fuller says that really only
the USN solved the direct fire problem and that late in the war, but high
cross-rates were still a problem for the predictors. He adds that the
Germans solved it earlier, but found that even their high quality clockwork
time fuzes negated the benefits of precisely tracking a target. These
fuzes had only a 2 to 3 % error compared with 8% in a combustion fuze but
it was still not good enough. In 1944 a German mathematician showed that
the probability of a direct hit from an aimed non-timed fuzed shell was
better than a lethal burst from an aimed time fuzed shell. They went back
to that and Allied losses to flak increased substantially.
He also notes the Germans had the best ship AA fire control systems in
heavy cruisers and above of the war, but linked to an inadequate 10.5 cm
gun. PRINZ EUGEN 's AA was tested in US waters post-war, and her German
crew allowed to do an AA shoot, doing better than their counterparts in an
accompanying US cruiser.
Regards,
Barry
Iberian
follow:
> The single 20 on a pedestal had a crew of 5.
Now, this really kills me. Wow! This beast was just a beefy machine gun!
I've never imagined that a 20mm mount could need that many people around.
IMHO five guys should have stepped on each other feet a lot. What really
surprises me is that they needed a range setter for their sight. Since both
the Oerlikon and the Bofors were really close defence system, I am betting
that there was little need of a range estimation. With the range of a 20mm
machine gun you just need to see where your tracers are going and try to
hose down the target. What is the purpose of this range-setting in these
short-ranged Oerlikons? Am I wrong?
<snip>
> war. The 40s (except singles) had a separate director near each gun (one
> for each ). The idea was to keep the director aimer out of the smoke and
> vibration of the gun.
Now, that was really a good point. Thank you!
<snip>
>( or did they get a proximity fuse for the 40?) Anyway, the range just
wasn't a big deal.
If my info is correct (mainly from Norman Friedman's US Destroyers), the
40mm rounds did not have any VT fuse (proximity fuse). The smallest calliber
to be VT were the 3". Anyway, I tend to agree with you in that range wasn't
a big deal for the 40mm Bofors. But...... what was the purpose of having a
telemeter in the Mk-51 director then? On the other hand, if the Bofors gun
were supposed to deal only with aircraft coming at you (in contrast to
aircrafts coming at other ships in the proximity), what is the purpose of
computing a lead for the mounts? The only place were they would need to
generate a lead was in trying to shoot down crossing targets (aiming for
other ships), but it looks like the Bofors had only enough range to protect
itself.
The reason I am making these questions is that, judging from WW2 images,
short ranged AA fire looks to be massive, but little precise (it really
looks like thousands of bullets being hosed everywhere). This just doen't
fit wiith the idea of director range-estimated and aimed fire.
Any thought?
Best Regards,
The Iberian.
ANGIE-ANNETTE CAREW
<snip>
>On the other hand, if the Bofors gun were supposed to deal only with
>aircraft coming at you (in contrast to aircraft's coming at other ships
>in the proximity)
Not true Im only speaking from experience now, I was a first loader on a 40
MM twin mount during WW II we took our AA training at Mission Beach Calif
just out side of SD California. Most of our training had to with aircraft
passing in front of us (a towed target)
>, what is the purpose of computing a lead for the
>mounts? The only place were they would need to generate a lead
>was in trying to shoot down crossing targets (aiming for other ships),
>but it looks like the Bofors had only enough range to protect itself.
We started out our training shooting "trap" and you have to learn to lead in
trap shooting.
How about you shoot down my attacker and I,ll. shot down your attacker. In
other words if it moves kill it ?
Jim Carew
B F Lake
//looks like thousands of bullets being hosed everywhere). This just doen't
fit with the idea of director range-estimated and aimed fire.
Any thought?//
Someone should help out here. It started with barrage fire with pom-poms,
where you had shells that went off at a certain range (self-exploding), so
you needed to know the range of the incoming plane and its range rate to
know when to fire your barrage so it would go off just in front of the
plane. This was more complicated using timed fuzes, so you could move the
barrage closer as the planes kept coming and you kept firing. So range
really mattered in barrage fire. By 1941 the RN was using a radar equipped
(282 radar) pom-pom director in a separate tub from the multiple pom-pom
mounting, I don't know if there was a timed fuze choice of ammo. If there
was then they would also need an auto fuze setter to go with the range
computer as existed with bigger AA guns. The Bofors 40 and its director
did the same job only a lot better. Effective range depended on the type of
ammo used, most useful range about 2,800 yds. So, if using contact fuzes,
then want to know range to start shooting so you don't start too soon. If
barrage, as above. There was lots of info on the ammo choices here last
year, maybe someone can refresh this for the 40 and 20 wrt the need for
range info. As regards lead angle for crossing target, ok who cares for
point defence, but a lead angle is also required in elevation if the target
stays high and closes, also the trigonometry of the fire control solution
needs range for the lead angle (larger angle if plane closer etc) But the
40 also had an HE-Tracer ammo, so ? It is true the RCN 40s post war
dropped the radar from the war, so maybe it just wasn't worth the bother,
and during the war they were trying too hard but nobody wanted to take the
chance that it was not in fact needed? Anyway there are people out there
who know a heck of a lot more about this than I, so lets hope they come to
the rescue here :(
Regards,
Barry
tonywill...@my-deja.com
"B F Lake" <bfl...@coastnet.com> wrote:
> (Somewhere, there should be a really explicit exposure of whatever
people
> were causing the really bad RN gun development and production in the
> 30's/40's! Inability to figure out how to elevate guns to make them
dp,
> not powered, etc etc- compares with US torpedo testing lab as a thing
to
> really hate )
There is an interesting document in the MoD Pattern Room, entitled
"Report of Naval Anti-Aircraft Gunnery Committee 1931". I enclose the
following extract from it, taken from my forthcoming book on the
development history of heavy automatic weapons and their ammunition:
"Even at the beginning of the 1930s there was some concern about the
adequacy of the British weapons. The problem was considered by the
Naval Anti-Aircraft Gunnery Committee, which produced a report in April
1932.
The Committee went into great technical detail in calculating the
effectiveness of different guns. They took into consideration such
matters as the nature of the threats, the time during which aircraft
could be brought under effective fire by different weapons, the range
and rate of fire of the guns, the effectiveness of shells and fuzes, and
appropriate methods of fire control. Their conclusions make interesting
reading.
Three types of attack were considered; precision (i.e. level) bombing,
torpedo bombing, and close-range attack with bombs or machine guns.
With remarkable prescience, the Committee also identified a further
potential risk:
"The possibility of explosive aircraft being manoeuvred by human
pilots to hit ship targets cannot however be ruled out. It is reported
that, sooner than accept defeat, ramming other aircraft is a recognised
principle among Japanese pilots.
Note:- The Air Ministry regard this idea as exceptionally secret
and would prefer that it be not generally promulgated"
It was clear that the Committee considered such attacks to be
potentially extremely difficult to deal with, a concern fully justified
by the experience of a dozen years later.
In considering short-range defence, the Committee was most concerned
about torpedo bombers, calculating that any weapon system able to cope
with them would be able to deal with other forms of short-range attack
easily enough. Exercises between 1928 and 1931 had shown that the
probability of a torpedo bomber hitting a ship was only 10% at 1,250
yards (1,140m) but rose to 30% at 1,000 yards (910m), 50% at 750 yards
(690m) then increased very sharply to 85% at 600 yards (550m).
This led to a demand for a range of 2,500 yards (2,300m) from automatic
AA guns, in order to achieve the aim of certain destruction of an
aircraft with 10 seconds of firing at a mean range of 2,000 yards
(1,820m). It was estimated that an aircraft dropping a torpedo from
1,200 yards (1,100m) would already have been under fire from such
weapons for 17 seconds, which was assumed to be more than enough time to
shoot it down.
The two existing weapons - the .5" machine gun and 2pdr - were
considered in detail. There were strong indications that the Committee
was not much impressed with either, suspecting that the .5" was
ineffective and that the 2pdr Pom Pom (yes, that was the title they gave
it!) had too low a muzzle velocity. They were also concerned about the
2pdr's rate of fire. This was felt to be just about adequate in its
8-barrel form but the Committee recommended that no further steps should
be taken to develop the 4-barrel version, which was all that smaller
vessels could carry.
They expressed a hope that both guns would be replaced by an
intermediate calibre with a 760m/s muzzle velocity and a total output of
at least 1,250 rpm, and recommended a series of trials to determine the
ideal calibre.
In fact, two experimental weapons emerged. One was the very powerful
Vickers .661" heavy machine gun developed between 1935 and 1938, which
was intended to be fitted in a six-barrel mounting. Development was
cancelled in 1938 in favour of the 20mm Oerlikon S, which had the
advantage of firing the explosive shells which were by then regarded as
essential. The other, somewhat closer to the Committee's views, was the
35mm 1½ pdr Mk V, which fired a 0.68kg shell at 790m/s. However, the
eight-barrel mounting ended up weighing more than the 2pdr's, and the
weapon was cancelled in 1937.
Later on, a more powerful "high velocity" loading of the 2pdr was
introduced which raised the muzzle velocity to 730m/s, partly achieved
by reducing the shell weight from 0.9 to 0.76kg. This could only be
fired in modified guns and the "hot" high-pressure loading cannot have
done much for the reliability. The rate of fire was also increased to
115 rpm."
(From "Rapid Fire" to be published by Airlife, UK, in April 2000)
> A note from Thomas Fuller says that really
only
> the USN solved the direct fire problem and that late in the war, but
high
> cross-rates were still a problem for the predictors. He adds that the
> Germans solved it earlier, but found that even their high quality
clockwork
> time fuzes negated the benefits of precisely tracking a target. These
> fuzes had only a 2 to 3 % error compared with 8% in a combustion fuze
I have read different figures for ground-based AA; 2% for powder fuze,
0.5% for clockwork.
Tony Williams
Sent via Deja.com http://www.deja.com/
Before you buy.
Iberian
<snip>
> We started out our training shooting "trap" and you have to learn to lead
in
> trap shooting.
Jim, thanks for your answer. Could you explain what this shooting "trap"
involved? Was the lead computed in the 40mm with a precise method or was it
just a broad estimation? How was the range computed? Was it common to use
local control in contrast to remote control by the Mk-51 director? Were the
40mm fuses time-setted or were they contact-only?
The Iberian.
ANGIE-ANNETTE CAREW
Iberian <NoMail...@NoMoreSpam.Com> wrote in message
<snip>
>>We started out our training shooting "trap" and you have to learn to
>>lead in trap shooting.
> Jim, thanks for your answer. Could you explain what this shooting "trap"
> involved?
You use a shot gun to shoot at clay "pidgins" thrown at various angles in
front of you usually by a machine.
>Was the lead computed in the 40mm with a precise method or was
>it just a broad estimation? How was the range computed?
Broad estimation when we were on local control. How much to lead a target is
something you learn by doing. Thats why they started us out on trap shooting
its a lot easier and cheaper than jumping right in and learning how to lead
a target on a twin mount 40MM. As far as the range goes as I remember
when we were on local it was done by the persons handling traversing
and the elevating im not sure which one, remember were talking over
50 years ago so its hard to remember details like that
>Was it common to use local control in contrast to remote control by the
>Mk-51 director?
Its been over 50 years ago that I shot a 40MM I can,t remember, but most of
our training was naturally on local so we could lean to work as team.
>Were the 40mm fuses time-setted or were they contact-only?
I,m not for sure, for the same reason as above, as I recall we had a
four round clip one was tracer, one was armor piercing, one solid,
and one that exploded on contact weather that was time fused or
not I cant remember.
Jim Carew
B F Lake
//(From "Rapid Fire" to be published by Airlife, UK, in April 2000)//
Sounds good! Roskill mentions here and there that he was in the
department looking at AA and said something wasn't right with RN predictors
compared with US and German ones- any details?
I gather the pom-pom's problem was the loading where too much stress came
on individual shells and on the belt links so mv had to be kept low.
Bofors top loading sytem allowed higher mv and good reliability in action?
G Brooke in "Alarm Starboard" says the pom-poms in PoW failed (this when
ship fighting for its life!) because shells broke up, jamming the guns.
Any details on that?
The 1931 committee seems to have been on the ball, so who filed their work
under "forget"?
Thanks,
Barry
B F Lake
realistic for real life, which is in question, so we need more opinion. A
factor here is that in practice shoots, they used a plane towing a sleeve
target on a wire. To keep the plane safe you need to be shooting at the
target with a good spread between, which is best with a crossing target.
In "modern" practice AA, the T-33 comes straight in high, towing a little
plastic target on a long wire, but you have to wait till the plane is
nearly overhead so the target has a goodly vertical angle between it and
the plane. So the question is what happened out in the Pacific?
The drill was where a circular ASW screen was around the carrier or
whatever main body, when you got an air raid warning, the circle was
shrunken in so all the screening ships were close to the main body. Then
an escort by firing at a plane approaching the carrier in the escort's
sector would essentially have a point defence problem as though the plane
were attacking it. This leaves the question whether a plane would be
engaged crossing ahead say heading for the carrier, or whether it would be
out of range of the 40s by the geometry of the formation the ships were in.
Anybody know details of this?
Trouble with the whole idea is if a sub came along while you were in air
defence mode, you were all just one big target in the middle instead of
having a screened main body. Also when the air attack became a lobbing in
of a tactical nuke, you didn't want to be bunched together either. Whole
thing became to spread out, and have longer range point defence for each
ship instead of mutual support concentrated gun fire. Area AA missile
nice if you've got 'em thing too. This left the ASW screen in tatters
though, so idea to fool sub by disguising main body ship noise with DD-like
noisemaker. Also to hide the main body from air attack by making escorts
look bigger on radar (noble sacrifice <g> ) and not putting main body in
middle of group etc. All too difficult!
The Kamikaze team in 1945 that produced the 3"/50 with its Gunar FC
computer, set it up to handle targets coming straight in best, and it was
weak on crossing rate targets ( you had to make a choice it seems) , so it
was a point defence gun and longer ranged than the 40s, so does this
indicate there was no crossing target requirement for the 40? or is it an
unrelated matter?
Thanks,
Barry
Ogden Johnson III
<OTH...@prodigy.net> wrote:
>You use a shot gun to shoot at clay "pidgins" thrown at various angles in
>front of you usually by a machine.
The Chinese invented trap shooting? I didn't know that.
OJ III
[Use cpcug dot org for email. This is posted via a trial ISP.}
Malcolm Hopkins
>I have read different figures for ground-based AA; 2% for powder fuze,
>0.5% for clockwork.
>
>Tony Williams
>
>
The clockwork fuse timers must have been an incredible piece of design
cunning to be able to withstand the G forces of firing and be so
accurate.
I remember reading an article about modern proximity fuses that were
in fact miniature Radars that fitted in the miniscule space available
in the shell. The photographs showed it utilised a flexible "pcb" syle
wiring loom to connect the various elements together ie: antena,
battery, computer, enertia switch, detonator etc.4
Malcolm Hopkins
Wellington
New Zealand
Please remove "no.spam" from address to reply
ken...@cix.compulink.co.uk
(B F Lake) wrote:
> Effective range depended on the type of
> ammo used, most useful range about 2,800 yds. So, if using contact
> fuzes,
> then want to know range to start shooting so you don't start too
> soon
The commonest British Bofors ammo was HE tracer. This was contact
fused with the shells self destructing at 3000 to 3500 yds. This could
be increased to 7000yds in some. SAP ammo was also available
tonywill...@my-deja.com
> //(From "Rapid Fire" to be published by Airlife, UK, in April 2000)//
> Sounds good! Roskill mentions here and there that he was in the
> department looking at AA and said something wasn't right with RN
predictors
> compared with US and German ones- any details?
I'm not an expert on predictors but IIRC the best type used a triaxial
system (someone else can fill in more details!). The RN were developing
one of these interwar but it was stopped for lack of funds, which meant
that the RN had to purchase the USN's triaxial system (Mk 37?) when the
war came along. Can't comment on the German ones but I would expect
them to be efficient; they even had stabilised 105mm gun mountings (what
luxury!).
> I gather the pom-pom's problem was the loading where too much
stress came
> on individual shells and on the belt links so mv had to be kept low.
> Bofors top loading sytem allowed higher mv and good reliability in
action?
> G Brooke in "Alarm Starboard" says the pom-poms in PoW failed (this
when
> ship fighting for its life!) because shells broke up, jamming the
guns.
> Any details on that?
The 2pdr's mv was low because the case capacity was small; it was only
158mm long and slim, whereas the Bofors' was 311mm long and fatter; so
it carried about twice as much propellant. The Bofors action was
certainly more reliable, but the separation problem was simply down to
the crimp not being strong enough to take the rough handling.
Another problem with the 2pdr in the PoW action was that the shells
weren't fitted with tracers, so had no deterrent effect. Bofors and
even 20mm tracer fire were seen to distract the Japanese pilots.
> The 1931 committee seems to have been on the ball, so who filed
their work
> under "forget"?
The politicians, of course, aided and abetted by the Treasury. The RN
knew its business but never had enough money, until just before the war
when it was too late for new developments, hence the Oerlikon and Bofors
were purchased off the shelf from abroad (fortunately, they were both
very good).
B F Lake
//The 2pdr's mv was low because the case capacity was small; it was only
158mm long and slim, whereas the Bofors' was 311mm long and fatter; so
it carried about twice as much propellant. The Bofors action was
certainly more reliable, but the separation problem was simply down to
the crimp not being strong enough to take the rough handling.
Another problem with the 2pdr in the PoW action was that the shells
weren't fitted with tracers, so had no deterrent effect. Bofors and
I have a note that says pom-pom ammo was "Short cased round with HE and
HE-Tracer" so does this mean PoW just wasn't using the tracer or is my note
wrong?
Another note with ref Garzke WW2 Allied BBs, says pom-poms had trouble
with deflective clips, details not provided.
Notes say the basic feed system using disintigrating metal links could
only stand so much pressure, so mv had to be kept low, the cases subject to
being damaged as the pawl pulled the belt through.
Main trouble was the violent way the cartridges were extracted from the
belt by the upper extractor as the bolt recoiled, when the ejector knocked
the cartridge loose so the bolt could take it up and push it into the
chamber for the next shot, the spent case having already gone through the
same process. The action frequently caused the shell to become loosened
from the cartridge case, and sometimes led to de-bulletting as the
cartridge was thrust forward and met the guide ramp leading to the chamber.
The loose shell might get pushed free of the case or it might kink or
deform the case mouth enough to prevent the case from properly seating in
the chamber. This would require an armourer to clear the jam if re-cocking
failed to clear it. The Bofors gravity feed system was much superior.
A further note says that in the old cloth belt system, the belt took the
strain, but with the 14 round metal belt, and 10 belts being linked, used
in the Mk II*C, and after, where each round bears the weight of the
following rounds, so the strain on the cartridges in the first belts would
be very great.
The 1922 Mk VIII had a too-low mv of 2040 f/s, but was found to be strong
enough to be able to take an increase to 2400 f/s in 1937. (which killed
the 1.5 pdr Mk V project, whatever that was)
So one could argue that the crimping of the shell to the cartridge was too
weak or that the action was too strong! Since the old cloth belt WW1
pom-poms had malfunctions and breakages, it seems the real fault was
persisting with this action using metal belts and improving the pom-pom
instead of trying something totally new instead of the 1922 Mk VIII
specially designed for multiple mounts including the big 8 barrelled
mounting. Besides needing a low mv for less violent recoil, the belt
system required a small case? So a gravity feed would work with a bigger
case and more mv, range, (heavier shell?) , and less subject to jamming, if
I understand it right.
Regards,
Barry
ANDREW BREEN
>//The 2pdr's mv was low because the case capacity was small; it was only
>158mm long and slim, whereas the Bofors' was 311mm long and fatter; so
>it carried about twice as much propellant.
Pom-pom ammunition had a case of approximately the same diameter as the
round, and about half as long again as the round. The whole thing (case+
round) is about the same height as a softback book (says he, measuring a
book against the WW1 pom-pom shell that I use as a paperweight :)
The Bofors round is longer (the round and the case are both longer)
and the case has a coke-bottle shape.
> The Bofors action was
>certainly more reliable, but the separation problem was simply down to
>the crimp not being strong enough to take the rough handling.
My father's experiance was that the single pom-pom was a very
reliable and rugged weapon, but there were nasty stories about
misbehaving guns in the multiple (quadruple and octuple) mountings.
Could it be that the feeds in the multiple mounts placed more
stress on the belt?
I asked my father about the single pom-poms in coastal forces craft,
and he reckoned that they had far more trouble with Oerlikons jamming
than pom-poms (they _did_ have problems with shells bursting prematurly
as they left the pom-pom - scartch another flash eliminator :(
> I have a note that says pom-pom ammo was "Short cased round with HE and
>HE-Tracer" so does this mean PoW just wasn't using the tracer or is my note
>wrong?
Pom-pom AA load was self-destructing HE, with every fourth round a tracer.
Coastal forces load-out was HE, Incendiary, unfilled shell (as a proxy
for solid shot), HE, tracer. Sometimes extra tracer were loaded in.
--
Andy Breen ~ PPARC Advanced Research Fellow
Solar Physics Group, U-W Aberystwyth
"Usenet should require licenses;
licenses that can be revoked." (Abigail, in the Monastery)
Bertil Jonell
Iberian <NoAd...@IamTiredOfJunkMail.com> wrote:
>If my info is correct (mainly from Norman Friedman's US Destroyers), the
>40mm rounds did not have any VT fuse (proximity fuse).
Correct. The 40 didn't get a proximity fuze until the 70's.
-bertil-
--
"It can be shown that for any nutty theory, beyond-the-fringe political view or
strange religion there exists a proponent on the Net. The proof is left as an
exercise for your kill-file."
B F Lake
//and he reckoned that they had far more trouble with Oerlikons jamming
than pom-poms //
I think it was a Nevile Shute novel where the girl was a Wren 20mm tech
and had to work on the guns when the ships came in and frequently clear
jams for them, seems the operators weren't as careful as they should have
been or something. ( ISTR thats the one where she shoots down a German
plane that was later thought to be surrendering and it drove her nuts after
worrying about it)
Regards,
Barry
tonywill...@my-deja.com
HE and
> HE-Tracer" so does this mean PoW just wasn't using the tracer or is my
note
> wrong?
Tracer was available but it seems wasn't used in PoW, according to the
Gunnery Officer's report.
> The 1922 Mk VIII had a too-low mv of 2040 f/s, but was found to
be strong
> enough to be able to take an increase to 2400 f/s in 1937. (which
killed
> the 1.5 pdr Mk V project, whatever that was)
This was only achieved by reducing the projectile weight. They squeezed
as much performance out of the cartridge as they could.
> Since the old cloth belt WW1
> pom-poms had malfunctions and breakages, it seems the real fault was
> persisting with this action using metal belts and improving the
pom-pom
> instead of trying something totally new instead of the 1922 Mk VIII
> specially designed for multiple mounts including the big 8 barrelled
> mounting.
The 8-barrel mounting came out of calculations concerning the rate of
fire required to down a torpedo bomber before it came too close.
The Bofors gravity feed system was certainly more reliable, but limited
the ammunition capacity. It was reloaded with 4-round clips, which
lasted less than two seconds. Just imagine the scene during a battle,
with dozens of loaders scurrying to and fro trying to keep an 8-barrel
Bofors mounting going!
> Besides needing a low mv for less violent recoil, the belt
> system required a small case? So a gravity feed would work with a
bigger
> case and more mv, range, (heavier shell?) , and less subject to
jamming, if
> I understand it right.
This may be true, but I don't believe it happened like that. The 2pdr
was just the last in a line of pom-poms, its immediate predecessor being
the 1.5pdr which used a bottlenecked case. The 2pdr was simply created
by straightening the case to take a larger (40mm) projectile. The
muzzle velocity wasn't deliberately kept low; it was simply as much as
could be squeezed out of the small case. And it was belt-fed because
the pom-poms had always been belt-fed; the steel-linked belts were
intended to be an improvement over the cloth ones which tended to swell
up when they were wet, etc.
The Bofors was acknowledged to be a better idea as soon as it was used
in action. The PoW carried one of the first RN Bofors, an Army-pattern
aircooled single. The RN "borrowed" as many of the Army guns as they
could get hold of until the purposed-designed water-cooled twin
mountings came along (in 1942, IIRC).
B F Lake
IIRC) says Brits delivered a Bofors and its predictor to New York late
1940. RN was adopting Army 40s from ~ 1941, but these were the single
unpowered mounts on pedestal. RN twin seen in 1943-4 utility DDs by the
torpedoes in place of previous classes' quad pom-pom. OK , so that means
the 40mm delivered in 1940 must have been a twin or it wouldn't have had a
predictor (goes with remote power, which needs powered mounting, and single
wasn't powered) so does this not say the army had a powered twin in 1940
with a predictor (that the USN copied and had in ships late 1942), and so
why did the RN take so long -3 or 4 years to get it to sea? Also, the RN
twin had the 282 radar on the mounting, so was there a separate
predictor-can't find one- (I know they were working on the "self training
" mount that came out in 45) The 282 was used with a separate director for
quad pom-poms. The self- training twin 40 used a round parabolic antenna.
Thanks,
Barry
Jim Webster
> The Bofors was acknowledged to be a better idea as soon as it was used
> in action. The PoW carried one of the first RN Bofors, an Army-pattern
> aircooled single. The RN "borrowed" as many of the Army guns as they
> could get hold of until the purposed-designed water-cooled twin
> mountings came along (in 1942, IIRC).
They didn't borrow them. AA Command traded them, 300 in all, while
resisting the navy's attempts to hijack the total production. They were
traded for 5.25" guns that were subsequently used for the defence of
London. AA Command was promised 3 twin mounts and an unspecified number
of single mounts. What the Navy had not realised was that churchill had
already ordered AA Command to hand over the guns anyway - and they still
owe AA Command the three twin mounts :-)
See Ack Ack by Major General Sir Frederick Pile
TTFN
Jim
Honorary Secretary
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Ken & Laura Chaddock
>
> Zimmerman's book on Tizard visit to States in 1940 ("Top Secret Exchange"
> IIRC) says Brits delivered a Bofors and its predictor to New York late
> 1940. RN was adopting Army 40s from ~ 1941, but these were the single
> unpowered mounts on pedestal. RN twin seen in 1943-4 utility DDs by the
> torpedoes in place of previous classes' quad pom-pom. OK , so that means
> the 40mm delivered in 1940 must have been a twin or it wouldn't have had a
> predictor (goes with remote power, which needs powered mounting, and single
> wasn't powered) so does this not say the army had a powered twin in 1940
> with a predictor
No, the Royal Army introduced the Kerrison (Col K. E. Kerrison)
predictor and remote control system for the 2 pdr AA in 1937. This
(quite effective) system was adapted to the Bofors when it came into
RA service in 1938. This is most likely what is being refered to.
(that the USN copied and had in ships late 1942), and so
> why did the RN take so long -3 or 4 years to get it to sea? Also, the RN
> twin had the 282 radar on the mounting, so was there a separate
> predictor-can't find one-
This was the "Hazemeyer" which was a Dutch development (Hazemeyer was
a subsidiary of Siemens Halske). When the Germans invaded the Dutch sent
all the plans and the only known mounting (on board the minelayer
Wilhelm
van der Zaan) to Britian where it was further developed.
Primary ranging was via the type 282 Radar but there was an optical
sight and an on mount predictor and could use open sights as well. The
mount was well thought out and very effective but the technology wasn't
ready and it proved very unrelieable.
> (I know they were working on the "self training " mount that came out
> in 45)
This was the STAAG (Stabilized Tachymetric Anti-Aircraft Gun) though
most of the gunners had many rather less printable namesfor it. The
mount
was unrelieable, inaccurate and often dangerously unstable. The only
known
success in shooting down and aircraft came during the Suez Crisis when
an RN STAAG shot down an RAF Hunter jet fighter.
...Ken
B F Lake
// snip good info//
OK, so the 4 RCN DDs -V's from 44 and the Cs from 45 came with the
Hazemeyer twin 40 and 282, but by Korea some had twin 40 there with a
separate optical director right by it on the platform. The Tribals had
this too. The frigate conversions in the 50s also had this with the
director up on the QM's shack. ~1950 ONTARIO got these directors for the 4-
40 quads that replaced the quad pom-poms and these went in the 4 tubs that
had had the 282 fitted pom-pom directors. Now these seem to have been
same as wartime USN fit, so if those via Tizard, does this mean these were
1937 Kerrison predictors??! (Did we do the whole war without, and then
fit pre-war gear finally post-war???? ) I wonder if they swapped the
whole twin 40 for USN one or just stripped it of the radar etc?
There is a (night?) photo of a Tribal using twin 40 for shore bombardment
in Korea, so it got used anyway.
Thanks,
Barry
tonywill...@my-deja.com
"B F Lake" <bfl...@coastnet.com> wrote:
The late-war and postwar twin-Bofors in RN service wasn't an American
one, it was the British Mark V, a simpler design than the Hazemeyer.
Can't comment on the director used but those in use in the 1950s weren't
necessarily better than those developed in the 1930s, except for the
addition of radar where appropriate.
B F Lake
//The late-war and postwar twin-Bofors in RN service wasn't an American
one, it was the British Mark V, a simpler design than the Hazemeyer.
Can't comment on the director used but those in use in the 1950s weren't
necessarily better than those developed in the 1930s, except for the
From photos, it appears the RCN post war twin 40 and director was the same
as the RN fitted in C class in place of Hazemeyer twin, and in some other
RN applications (T class limited conversions, Later Battles in place of
some STAAGs on the platform between torpedo tubes etc). The RN had a
different powered mount for 40 singles. As an example of what was going
on, the brand new ONTARIO was completed in April 45 with no Bofors (and was
delayed a year anyway from shortages of steel) . She scrounged 4 single
pedestal type ~August ( probably in Alex) on way to Far East, and planned
to get some more in Australia had the war gone on. ( in place of 20s)
She did have a newer sort of quad pom-pom than pre-war version as seen from
the upper and lower barrels being in line vertically while the upper two
are still set back-was this mounting better than older off-set both ways
version?
It looks like the RN had the twin STAAG, the above twin, and possibly a
third version that went in the Type 12s before Seacat?
Regards,
Barry
Ken & Laura Chaddock
>
> Ken wrote:
> // snip good info//
> Hazemeyer twin 40 and 282,
No these guns were the Mk 5 twin mount which was a simplified twin
designed to use the RP50 metadyne for remote FC or the Mk 7 Stabilized
ring sight for local control. They were more reliable than the Hazemeyer
(which was officially the Mk 4) and easier and cheaper to produce.
It's ironic that the STAAG replaced the Mk 4 Hazemeyer and was later
replaced with an even simpler MK 5 which is still (?) in service in some
older vessels where it replaced STAAGs.
but by Korea some had twin 40 there with a
> separate optical director right by it on the platform. The Tribals had
> this too. The frigate conversions in the 50s also had this with the
> director up on the QM's shack. ~1950 ONTARIO got these directors for the 4-
> 40 quads that replaced the quad pom-poms and these went in the 4 tubs that
> had had the 282 fitted pom-pom directors. Now these seem to have been
> same as wartime USN fit, so if those via Tizard, does this mean these were
> 1937 Kerrison predictors??! (Did we do the whole war without, and then
> fit pre-war gear finally post-war???? ) I wonder if they swapped the
> whole twin 40 for USN one or just stripped it of the radar etc?
Mk 5 were produced in Canada in numbers and were fitted in Ontario
and
Quebec, Warrior, Magnificent, the V and C destroyers and the Prestonian
class frigates. This mount was in turn replaced by the 3"50 Twin in the
destroyers which were converted to ASW ships in the mid 50s.
...Ken
tonywill...@my-deja.com
from
> the upper and lower barrels being in line vertically while the upper
two
> are still set back-was this mounting better than older off-set both
ways
> version?
> It looks like the RN had the twin STAAG, the above twin, and
possibly a
> third version that went in the Type 12s before Seacat?
I think that the late-war Mk V and the STAAG were the only twin-Bofors
mountings to see postwar British service. I'd have to check on the 2pdr
mounting (my sources are currently far from my internet link!). The
best source on WW2 naval weapon developments is Campbell's book (Naval
Weapons of World War 2); it's worth looking out for.
B F Lake
//> OK, so the 4 RCN DDs -V's from 44 and the Cs from 45 came with the
> Hazemeyer twin 40 and 282,
No these guns were the Mk 5 twin mount which was a simplified twin
designed to use the RP50 metadyne for remote FC or the Mk 7 Stabilized
The photos show the V's in 44-5 with the twin 40 and the 282 on top.
Also photo of CRUSADER in Dec 45. So CRESCENT out earlier would have that.
CRUSADER and SIOUX had refits ~1950 and photos after that show what I
gather now is the Mark V twin and Director on the platform just forward of
the gun. I am not sure if ALGONQUIN and CRESCENT ever got this mod before
they went in for their ASW conversions , I suspect not.
//They were more reliable than the Hazemeyer
It's ironic that the STAAG replaced the Mk 4 Hazemeyer and was later
replaced with an even simpler MK 5 which is still (?) in service in some
Yes , Battles , or some of them, started with two STAAGS on platform
between tubes, later photos show one Mark V and director there. Still with
STAAGS in X position though.
//Mk 5 were produced in Canada in numbers and were fitted in Ontario//
ONTARIO from 1950 did not have twin 40s, only quads and singles. I do not
know the marks, so was the quad also Mark V ( two put together?) A guy
who was a quad pom-pom captain in her in 1946-7 said they tried to put a
twin 40 on the 20 platform below the bridge (above the pom-pom) but the
platform couldn't take it so it was removed. I have seen no photo of that
and I kind of doubt it as there is no room there and the 1950 photo shows
the empty platform ( aft of the signal lamp) same as 1945 where a single 20
was.
//Quebec//
She got 2 quad 40s in Charleston refit 43-4when became RCN and took them to
the Pacific. Don't know what directors came with those. Did these
directors get switched post war? I don't know if she got any twins .
//, Warrior, Magnificent, the V and C destroyers and the Prestonian
class frigates//
Yes
//This mount was in turn replaced by the 3"50 Twin in the
destroyers which were converted to ASW ships in the mid 50s.//
The Tribals started with a quad pom-pom forward of X gun and abaft the
tubes. X was a 4" . Post war, the quad pom-pom was switched for the twin
40 and director. Various ships had various guns in ABXY but ended up with
3/50 instead of 4" in X, Squid in Y, and the twin 40 replaced by two
singles.
Any info on the director that went with the Mark V? Was it the same as
the USN wartime one? Was it the same as the gyroscopic sight for the USN
20s?( except that needed a range setter and this director was a one man
thing ISTR you got "in" with the bar around your back and swung it around
and up and down with your legs like it was a single 20 only no gun)Was it
in fact a 1937 Kerrison? Ken says the Mark 7 was for local control so I
assume that was on the gun mounting??
Thanks,
Barry
...
ken...@cix.compulink.co.uk
() wrote:
> its immediate predecessor being
> the 1.5pdr which used a bottlenecked case.
The only 1.5 I have been able to find was the experimental one. The
2pdr dated to WW1 and was developed from the original 1lb Maxim tree
cutter. This used an identical mechanism to the Maxim machine gun. IE
recoil with a toggle lock.
tonywill...@my-deja.com
ken...@cix.compulink.co.uk wrote:
> In article <806k16$uat$1...@nnrp1.deja.com>, tonywill...@my-deja.com
> () wrote:
>
> > its immediate predecessor being
> > the 1.5pdr which used a bottlenecked case.
> The only 1.5 I have been able to find was the experimental one. The
> 2pdr dated to WW1 and was developed from the original 1lb Maxim tree
> cutter. This used an identical mechanism to the Maxim machine gun. IE
> recoil with a toggle lock.
I have pasted an extract from "Rapid Fire":
"More powerful 37mm guns firing longer cartridges, such as the USN Heavy
One Pounder (37x137R), developed from the Maxim 1ź pdr, saw limited
service. Another US design which used the same 37x137R cartridge was
the McClean cannon. This was a gas-operated weapon which, despite
failing US tests, was purchased by Russia and Spain. In Britain the RN
1˝ Pounder (37x123R) was introduced in 1915 but saw little service as it
was soon eclipsed by a larger version, the Vickers two-pounder (2pdr) of
40mm calibre, named for the nominal two pound (0.9kg) weight of the
shell. By then, torpedo boats were evolving into destroyers and were
far too large to be damaged by such a weapon, so it was introduced from
the outset as an anti-aircraft gun."
There will be scale drawings plus ballistic data on all of these
cartridges in my book (hint...)