Fathoms 40 realistically simulates the operations of a German U-Boat during the last days of World War II (1942-1944). It combines the strategic elements of popular board games with the computer's ability to provide animated action and automatic scoring. You, the captain, must guide your Mark XXI U-Boat into the Allied shipping lanes, seek out tankers and freighters, avoid depth charges, torpedo the convoy, and return safely to Brest, France.
The game starts in strategic mode with a map display where you seek out a shipping lane to locate a convoy. Once a convoy is located the game shifts into tactical mode with a sonar display. As captain you can choose to operate in silent, normal or emergency running modes; to climb or dive; run on diesel engines or battery power; raise and lower the periscope; charge the batteries; reload torpedoes. Convoys are protected by destroyers and escorts that differ as to the number of weapons they carry and their sonar ability. The U-Boat can sustain damage to the engine room, battery room, torpedo room, torpedo tubes, rudder, periscope, dive planes. Damage limits what functionality the captain can utilise. Damage can be repaired by moving out of the combat zone and returning to Brest.
There are three patrol missions in each game. The number of ships in each mission will vary. There are three sets of six torpedoes available in each mission. Reloading torpedoes takes 20 seconds. A combination of keyboard and joystick controls are needed to navigate, view through the periscope and attack. After each game, the evaluation screen shows total victory points awarded, total tonnage sunk and gives a final rank. There are three levels of difficulty to master. The manual provides some history on U-Boats, and some useful strategy to consider on your missions - for example the speed of various ship types is provided, and what capabilities each ship has for detecting the U-Boat.