1) Club sandwich 2) Ship type 3) Triple-decker apartment house 
A three-decker is a sail warship which carried her guns on three fully armed decks. Usually additional guns were carried on the upper works (forecastle and quarterdeck), but this was not a continuous battery and so did not count. Three-deckers were usually `ships of the line`, i.e. of sufficient strength to participate in the line of battle, and.....
• (n.) A vessel of war carrying guns on three decks.
Three'-deck`er noun (Nautical) A vessel of war carrying guns on three decks. 
[n] - any ship having three decks 2. [n] - a warship carrying guns on three decks
noun a warship carrying guns on three decks