The only hidden weapons I have found is the Springfield in level 1(it isnt really hidden,
but it counts) and C96 mauser in the tank control room on lvl 5. It is in a safe that you
can either plant a charge on, or, as i recommend, you go above the control room and drop a
gammon grenade in, and that will both take care of most of the soldiers and open the safe.
WARNING: The C96 is a terrible pistol when it starts out and I would much rather recommend
the Colt .45 with all upgrades.

on level 5 in the tank factory control room where you have to shoot the control put a comp
b on the safe and after its blown up you will find the c96 mauser and on level 6 if you
land on the top floor of the house next to the green smoke flare there is a m18 recoiless
rifle

In level three there is a shotgun at the place like labyrinth. Its at the exit.