The first release of Sub Battle Simulator supported Hercules Monochrome and CGA 4 color graphics modes only. EGA 640x350 16 color support was added later for the Masters Collection release.
Sub Battle Simulator is the ONLY sub simulator for its time that includes aircrafts as opponents. You can choose to remain on the surface and defend yourself with your guns, or dive and hope to avoid the bomb and/or strafing that'll surely follow.