Call of Duty: Ghosts
The APS Underwater Rifle appears in the missions "Atlas Falls" and "Into the Deep", being used by Logan Walker, Keegan P. Russ, Thomas A. Merrick and Kick. Unlike other guns, the bullets will take time to hit their targets, rather than hitting them instantly, due to water slowing the bullets down. They will also leave a trail of bubbles.
Call of Duty: Black Ops 4
An APS Underwater Rifle is seen in the calling card "From the Depths" in Call of Duty: Black Ops 4.