U-Boot is a nice and simple game in which you control a submarine and your job is to explore as much as possible without crashing against various objects or being killed by various enemies. You will be equipped with a certain amount of torpedoes and mines to destroy enemies and obstacles, so you should use them wisely. As you advance in the game, the submarine will move more quickly, so you will need to be more careful. If you get killed, the game will be instantly over as you only have one life. There are, however, several bonuses and power-ups that you can collect on your way.
The game includes three modes: Sailor, Captain and Seawolf. In Sailor mode, you advance progressively in levels as you explore the ocean. In Captain mode, you need to reach a certain amount of points in order to advance in levels; while in Seawolf, you move very quickly, so it is for more advanced players. The game offers simple but attractive graphics, simple sounds, and very repetitive and annoying music.
To conclude, if you are looking for a simple but enjoyable game to pass the time, U-Boot may work for you.