Other militarisms (and they were legion) included "deep kim-chi"
(referring to the Korean comestible) and "in a heartbeat" (as in
"without hesitation").

I still use "jack-shit," though in some circles I replace it
with "diddly-squat" or "bupkas."  No,  didn't know THE Jack
:-).  He probably was PCS or TDY when I DEROS'ed his unit,
and I was probably in CBPO (pronounced CEE-BOH) when my squadron
was in his rear-view mirror.

And I wonder--

Did he have to suck rubber?  (That is, practice military exercises
while wearing a gas mask)

Did he ever eat bag nasties?  (Slang for MRE's--Meals Ready To
Eat--K Rats of the future, in plastic pouches)

Did he spit-shine his low-quarters?  Was he ever bedposted?  
Did he ever get called a sissy la-la?

If Jack answered two out of the three last questions--then Jack
is short for Jacqueline!  (Low-quarters are women's military
oxfords; a sissy la-la is a woman who acts wussy--that is, she
demurs from routine military activities, such as crawling under
barbed wire or diving into muddy holes.)

Shoot, I don't remember jack-shit...