The Caswennan was an erroneous name used to identify the airship the Prydwen in a pre-release exclusive published by Vanity Fair prior to the release of the Fallout TV show. Despite labeling the airship "Caswennan" in a captioned photo, the airship in the photo features "PRYDWEN" to the left of the Brotherhood of Steel decal on the forward section of the hull. The photo used in the Vanity Fair article and the corresponding scene in the television release are identical.
Behind the scenes
The name "Caswennan" is an alternative name used in some versions of the Arthurian legend for the ship sailed by King Arthur, more commonly known as the Prydwen.