https://en.wikipedia.org/wiki/APS_underwater_rifle

Under water, ordinary bullets are inaccurate and have a very short range. The APS fires a 120-millimetre-long (4.7 in), 5.66 mm calibre steel bolt specially designed for this weapon. Its magazine holds 26 rounds. The APS's barrel is not rifled; the fired projectile is kept in line by hydrodynamic effects; as a result, the APS is somewhat inaccurate when fired out of water.

Effective firing range 30 m at depth 5 m (98 ft at depth 16 ft)

20 m at depth 20 m (66 ft at depth 66 ft)

11 m at depth 40 m (36 ft at depth 131 ft)

Maximum firing range 100 m in the air

Also an anti-Kaiju weapon:

The rising threat of attacks by frogmen in naval bases caused various anti-frogman techniques to be developed.