Depth charges are a simple explosive devices fused by depth fuse, these bombs are dumped or launched from surface ship with a preset expositive depth. Most of those charges are barrel size dropped against submarines. Smaller versions are anti-frogmen charges, small as a standard hand grenade and can be toss as grenades. Before throwing them one had to specify the desired depth of explosion.
Guns' trigger is usually covered by a narrow strip called trigger guard. The job of the guard is to prevent any accidental pull of the trigger. Using thick gloves like divers wears can be problematic… some guns like the M-16 have a removable trigger guard for gloved palm. Guns designed to operate underwater are already have larger trigger guard.