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U.S. Department of Transportation U.S. Department of Transportation Icon United States Department of Transportation United States Department of Transportation

Escort Carrier

U.S. Maritime Commission type S4-S2-BB3

Before the United States even entered World War II, the U.S. Maritime Commission participated in the Allies’ desperate chase for aircraft carrier superiority. Planners were learning that military air cover was a crucial component of convoy protection but there were only a limited number of fleet aircraft carriers and the Allied navies could not commit them to escort duty.

As a solution to this shortage, the U.S. and the United Kingdom developed the concept of a small carrier designed to escort convoys. Many of the earliest escort carriers, including the United States’ Long Island and Bogue -classes, were converted by the Maritime Commission from C3 cargo ship hulls. These carriers were slow – capable of less than 20 knots – but more than capable of keeping up with merchant ships in-convoy.

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Maritime Commission type S4-S2-BB3, also known as the U.S. Navy’s Casablanca class, were the first purpose-built escort carriers.  These “baby flattops” were 490 feet long, and displaced about 6,890 tons.  They were noticeably smaller than the Navy’s fleet aircraft carriers, carrying about one-third as many planes, but because they had been designed as aircraft carriers from the beginning, they had several advantages over converted C3 hulls; a second propeller allowed the vessels to achieve 20 knots, a longer flight deck and separated machinery spaces.

The 50 S4-S2-BB3 type carriers were all built by Kaiser Corporation’s yard in Vancouver, Washington and many operated in the Pacific theater during World War II. Of the 11 aircraft carriers lost during the war, five were Casablanca-class escort carriers.


Bow view, showing control tower and flight deck.


Detailed view of control tower and flight deck.


Detailed view of the flight deck.


(Maritime Administration Heritage Asset, Object 2011.001R.0092)