A submarine simulator, or subsim for short, is usually a computer game in which the player commans a submarine. The usual form of the game is to go on a series of missions, each of which features a number of encounters where the goal is to sink surface ships and to survive counterattacks by destroyers. Submarine simulators are notable for the highly-variable pace of the game; it may take hours of simulated time to get into position to attack a well-defended convoy, and sub simulators typically include an option for players to adjust the ratio of real time to simulated time up and down as desired.