N-Sub is an arcade game released by Sega in 1980. It is similar to Nintendo's Heli Fire but currently nobody is sure which came first. It is also very similar to Deep Scan, except rather than control a boat firing at submarines, you're a submarine firing at boats (and other submarines). As it was a VIC Dual game, it was often bundled with another game in the arcade.
N-Sub is one of the few VIC Dual games to see a home console port — and one of Compile's first projects. It was brought to the SG-1000 in 1983, though as with all SG-1000 games, it only saw a release in Japan and PAL regions.