1. A fortified enclosure for artillery on a warship.
  2. An armored compartment for artillery on a rampart.
  3. (Fort.) A bombproof chamber, usually of masonry, in which cannon may be placed, to be fired through embrasures; or one capable of being used as a magazine, or for quartering troops.

The reinforced concrete casemates constructed by the Germans at Utah, Omaha, Gold, Sword and Juno beaches were effective in preventing Allied Naval fire from destroying German artillery, as is witnessed by the fact that many of those casemates still stand today, and show signs of numerous direct hits. Some of the casemates were dummies, and contained no artillery.