Well deck

[1] Late-20th-century commercial and military amphibious ships have applied the term to an entirely different type of hangar-like structure, evolving from exaggerated deep "well decks" of World War II amphibious vessels, that can be flooded for lighters or landing craft.

The earliest cargo steamers were flush deck with openings below rimmed only with low casings.

On 19 July 1941 Major R. E. Holloway, Royal Engineers, forwarded a design from a 1924 patent by Otto Popper of the Danube International Commission concerning a barge transporter for Danube barges.

The application of that idea to TLCs evolved into the British "Tank Landing Craft carrier" and that would become the Dock Landing Ship (LSD) that had an open, very deep and special purpose well deck open to the elements and thus technically a "well deck" in the traditional definition.

Previous barge carriers were of similar design to the military ships with a large stern well deck.

USS William Ward Burrows on 6 July 1942. Her 3"/23 guns have been replaced with 3"/50 guns and the sponson in the forward well deck for the 50-foot motor launches has been removed. (The aft well deck is clearly visible forward of the poop.)
The USS Indianapolis being overhauled at the Mare Island Navy Yard, 19 April 1942. Closeup view of her well deck area, from the port side. Note her forward smokestack, catapults, and Curtiss SOC Seagull aircraft.
Overhead view of USS Ashland 's well deck as she is moored pierside at Mare Island Navy Yard, 21 July 1943
An LCU approaches the well deck of USS Essex .