According to a news report that Anji, Fitz and the Eighth Doctor saw, the USS Delaware was a US Navy vessel that was once attacked 40 miles off the Libyan coast by EZ jet bombers. (PROSE: Trading Futures)
Behind the scenes
Although there have been several USS Delawares, none of the ones with decks were plausibly in service at the time of Trading Futures. Thus, this Delaware was a DWU-only craft.