From the rules: Each player tries to have his Cargo Ships safely deliver cargoes to certain ports, using his submarines both to protect his Cargo Ships and to sink enemy Ships and submarines.

Cargo ships are chosen randomly so their destinations change. Subs start on the S Marked on the map. Ships and subs move 1 space in any direction but cargo ships can gain distance by jumping friendly ships/subs and enemy cargo ships. When a sub jumps an enemy cargo or sub then it is considered sunk and taken for scoring purposes. Ships that make their destinations are set aside for scoring as well.

Play ends and scores are totaled when the last Cargo Ship makes it home port.