Russian Marines were recently spotting during a training drill using an underwater pistol and APS underwater assault rifle. The APS underwater assault rifle is a pretty interesting design that was developed during the early 1970s that fires steel bolts and has a magazine capacity of 26 cartridges.
From the MSN Article about the drill.
Aug. 28, 2014: Russian marines practice shooting underwater. They have been outfitted with state-of-the-art hydrosuits & masks to train for a secretive form of combat known as underwater sabotage. Photographer Andrey Nekrasov, a former soldier, took part in the drills. The 42-year-old, born in Bezhetsk in Russia, descended into seawater of 20 degrees, staying at low depths to complete shooting & mine-laying exercises.
Check out the APS Underwater Assault Rifle in action.