It just occurred to me today why the Weapons Control System (WCS) Mark I and II do not work with Gameport->USB adapters. They were built to pass through a keyboard as there was no other input for them to use at the time. I don't think it was until the time of the Gravis Gamepad Pro that the gameport was able to be split. Anyway, it likely just fired off key events, basically simulating key strokes. With this theory, it'd make sense why adapters ignore it -- they aren't designed for keyboards.
I think that the WCS can work with USB but it will need a different kind of adapter. Either a DIN->USB or PS/2->USB. If anyone has a WCS, try it out and let us know.
As a side note, I decided to get myself a USB throttle to avoid awkward keyboard configurations for each game, but some of you may want to indulge their nostalgia.
Cheers!