In the military - esp. those services with naval history - Heads refer to where the toilets are located - on sea, or on land. In similar manner, a wall
may be referred to as a bulkhead - though the two terms are technically unrelated.
The term Heads came from the days of sailing ships. It was first used in a nautical sense in Anglo-Saxon times, where it referred specifically to a
ship's figurehead - an ornately carved wooden decoration located at the front of the
ship. Often it was painted in great detail. However, by the 15th century, the term “
head” or “boat
head” referred to the entire front/bow of a ship,
boat, or other vessel.
In time, the term also came to be known by the
crew as a place to relieve themselves, which is probably around the same time that they began calling the front of a vessel, the Bow! Unless there was a stinking bucket under-decks, the only place for
crew to relieve themselves was at the heads - all the way forward, squatting on either side of the bowsprit. (The bowsprit being the part of the hull where the carved figure"
head" was attached.)