Dark Seas is a free print-and-play board game about nighttime warfare between naval forces in WWII. From the author:
Here’s a board game (as opposed to a miniatures game) featuring the night battles between naval forces in the Second World War. The game is designed for quick play, but with the intention of highlighting some of the key features of these battles. To play, you should have two six sided dice, a twelve sided die, a hex grid with large hexes, and adhesive-backed paper to make the counters. Optional, but highly recommended are some sets of colored wooden blocks of the type used by Columbia Games in their block games. These make very nifty counters that can be set on edge for ease of use. Below are the rules, a set of scenarios with maps, sheets to organize task groups, and a counter set.