From ZX Spectrum instructions As the commander of a submarine, it's your job to destroy four convoys, each consisting of a freighter and two destroyers. Having selected the difficulty level (Captain is easiest, Admiral is hardest) and the weather conditions (press F if you want fog to appear), press ENTER to start the game. You start the game docked on a friendly island. The top third of the screen shows the view through the periscope, while the bottom two thirds are taken up with four windows showing various pieces of information. (..) Your first task will be to locate an enemy convoy, indicated on the map screen. As your sub only has a top speed of 22 mph, you'll need to make use of the accelerated time feature (which speeds up the game by about 30 times) to cross the large map area quickly. Having sighted a convoy, you need to be within 1.5 miles to be able to hit them with a torpedo. The torpedoes travel twice as fast as the sub. Alternatively, you could fire a wire-guided missile, but this is rather harder to control. Once you've attacked, of course, the destroyers will be alerted. If you're on or near the surface they'll shell you; if you dive, they'll depth-charge you. Sitting on the sea bed with your engines off is a good way of fooling them into thinking you've left the area. However, you need to have enough compressed air on board to be able to blow the ballast tanks and return to the surface; if you run out of compressed air, you're stuck. Compressed air is produced by a compressor attached to the sub's diesel engine (which also recharges the batteries), but this can only be run on the surface. Underwater, you can only use battery power. You only have a limited amount of ammunition and fuel on board, so you'll need to return to a dock to rearm and refuel. The map gives the location and co-ordinates of your two docks. Docking is quite tricky and needs some practice! (Hint: going in slowly is a good idea...). You also have a time limit before the four enemy convoys cross the map and reach their destination.