GATO was a real-time submarine simulator published by Spectrum HoloByte in the 1980s for use on several platforms, including the Apple IIe and Atari XE Game System. It simulated combat operations aboard the Gato-class submarine USS Growler (SS-215) in the Pacific Theater of World War II. GATO was the first PC submarine simulator and the first simulator for the Apple Macintosh.
The player was tasked with chasing Japanese shipping across a 20-sector map while returning for resupply as necessary from a submarine tender. The islands on the map were randomly generated and not based on real-world geography. Combat was conducted using a screen with a view through the periscope and at various gauges and indicators. The game had multiple difficulty levels, the highest of which required the player to translate mission briefings which were transmitted only as audible Morse Code.
Source: Wikipedia, "Gato (computer game)", available under the CC-BY-SA License.