One of the earliest entries in the Avalon Hill "Adult Games" family, along with Gettysburg, Tactics II, Dispatcher, and Verdict. The basic game pits one U-Boat against one Destroyer. They maneuver around each other, with the Destroyer player having limited knowledge of the depth and position of the U-Boat, each attempting to score a critical hit to win the game. The multi-ship game pits three U-Boats against three Destroyers. The first set of rules (1959) came in booklet form while the revised rules (1961) were on a large, folded single sheet. Differences in the rules included where torpedoes could be placed and the damage caused by near-miss depth charge attacks. Board: A grid of 19 x 14 square spaces Pieces: 3 U-Boats, 3 Destroyers