Units represented in the game are individual ships of heavy cruiser size or larger, with provisions also given for convoys, submarines (specifically 'U-boats'), and air power.
While these are the essential statistics for surface vessels, this system keeps them all highly abstracted, as each is just a simple number, falling within a range of 0 to 9.
The Allied player's ports include England, the United States, Leningrad, "Russia" (actually Murmansk, on the Arctic Ocean), and Malta, in the Mediterranean.
[4] Minor rules include provisions for U-boat combat, the 'neutral port' of South America (which is where disabled ships in the South Atlantic sea area must go, and which they have to leave the following turn, lest the owning player lose points), convoys (which score additional points for the Allied player if they make it to England or Russia), and the possible internment of the Italian fleet if the Allies control the Mediterranean Sea for much of the game.
[5] Numerous variations (or 'variants,' to use the word preferred by Avalon Hill) were published for War at Sea in the years since it was released.
Among these variations are rules for the French Navy (which is interned early in the war), the Greek Navy, a third Russian port on the Black Sea, Allied mini-submarines (such as the 'X-craft' submarines that were used to attack the German battleship Tirpitz late in the war), and additional ships that were not represented in the original game.
These variations add simulation detail to the game (meaning that they made it more like the real war at sea), but at the expense of making it slightly harder to play.
"[13] In his 1980 sequel, The Best of Board Wargaming, Palmer described War at Sea and its sister Victory In The Pacific as "excellent introductory fare to entice newcomers into the hobby" with the former having a mere four pages of rules.
He praised the “honesty in advertising” by which War At Sea admits that it is only loosely a “simulation” in that it is based on “historical data” about ship design and is intended as a fun introductory game.