Linear warp drive is a variation on warp drive used in Federation starships, recognizable through the flattened, vertically oriented nacelles. One of the first production vessels using this technology was the USS Prospero, launched around 2265. (TOSS #23 "[/ Linear Warp Drive]") The first ship-of-the-line with this drive was the USS Decatur, the 2270 prototype of what became the Belknap class in the late 2270s. (Ships of the Star Fleet, vol. 1 [revised]) The USS Enterprise was upgraded to linear warp drive in its refit around 2273. (Star Trek: The Motion Picture)