General Dynamics Nassco recently began construction of a second mobile landing platform in its Barrio Logan shipyard.

The 765-foot-long ship will be what the U.S. Defense Department calls a “pier at sea” — a staging area that will serve U.S. Marines going ashore. The mobile landing platform has a high bow and a high stern, but an unusually low deck between them. Among other things, the ship will be able to serve as a base for U.S. Navy air-cushioned landing craft.

The ship will eventually be named the USNS John Glenn. Nassco plans to deliver the ship in the first quarter of 2014.

The builder reported that the first of the ships, to be named the USNS Montford Point, is 48 percent complete. Nassco has construction contracts to build three mobile landing platforms.