[John23832]

Yes. What's wrong with that?

A 9mm, buck shot, or even a 556 (which they are not using on a sub) is not piercing the pressure hull of a submarine. That's before considering all the other mass of metal and matter within the sub.

[esseph]

5.56 is fine in a sub.

Technically firing a .50 / 12.7mm should be fine for the hull even with API.

Bulkheads are thick.

(Note: SynTech / frangible ammo preferred)

[John23832]

I really meant that at the ranges that you would probably be engaging at in a sub (sub 10ft) a 556 is not the correct round to use.

[esseph]

Oh, valid!

Just thinking through Navy issued small arms. Lots of M4s and M17/M18.