After WW2 the US engaged in lots of experimental cannon designs, in calibres up to 37 mm.
One of these 37mm guns is quite well known - the T250 rotary gun for the Vigilante T249 AA system, which seems to have started with 37 x 256 ammunition (T250X-1) then changed to 37 x 219 (T250X-2) - was the second of these cartridges designated the T68 or was that just the case?.
There were two earlier guns, however: the T37 recoil-operated single-barrel gun, which was later redesignated the T171E2. The other was the T172E1 revolver cannon. The only info I have on the ammo for these guns follows: “The T172E1 gun was to fire the same [electric primed] ammunition as the T37E2, namely the T181 or T324 37 mm high explosive shell”.
I would be very grateful for any clarification concerning the ammo used in these guns!