A 9mm snubnose would be popular with combat troops, I'm sure. It could be carried inside their trousers, in a groin holster.
You access it by lowering your fly.
Don't laugh!
Most people, when they search a prisoner, are reluctant to really search the groin. An American soldier taken prisoner might still be so armed after a bad search by an insurgent.
He can indicate the need to urinate, moments after capture. Most captors will allow that much of prisoners, not wanting to endure the stench if they don't.
If the soldier is lucky enough to have only a couple of insurgents guarding him, they'll be off-guard while he turns away and lowers his fly. Come up with a 9mm snub, shoot the captors, grab their rifle and attempt to escape.
The chances of escape lessen with each minute after capture. In the first few minutes, you're still close enough to your lines to fellow Soldiers.
I knew an Air Force survival instructor years ago who told me of a pilot who carried a Colt .25 in such a way. He was never shot down, but it might have allowed him to escape if he were.
A revolver is absolutely reliable. If it fails to go bang, it's almost always the fault of the ammo. Today's revolvers are even more reliable, owing to coil springs and advanced design and metallurgy.
A 9mm snub would be handy in a thigh pocket, as a last-ditch gun. In very close quarters, such as in a vehicle, foxhole or when an enemy is physically clutching you, a snubnosed revolver can be a lifesaver.
My father told me that during the Battle of the Bulge, sidearms were at a premium by the troops who sat in foxholes. Wielding a rifle in a foxhole against an enemy who just jumped in next to you is nearly impossible.
A 9mm snub would be nice to have, and no problems getting ammo like with the .38 Special.
Make it stainless steel, with a shorter cylinder and the barrel coming back through the frame to the cylinder, and a 2-inch barrel. This would give you a total of about 3 inches of barrel, which would help velocity.
A 9mm snub would be a best-seller among service members.