Lionel introduced the 2333 Santa Fe F3 AA units in 1948. The F3 units were always sold in pairs or three car sets. The O gauge line the 2300 series numbers - 2333, 2343, 2353, and 2383) came with a double motored powered unit and a dummy A unit. The 027 2243 came with a single motor and a dummy B unit.
The different catalog numbers refer to mechanical changes made by Lionel. The 2333 had horizontal motors, while all the later units had vertical motors. The 2333 came with screen tops as shown above or louvered tops. The 2243, 2353 and 2383 came with louvered tops. The 2343 came either way.
Because the Lionel F3 units were top of the line trains, they always came with magnetraction. Either the powered A unit or the dummy A unit always had a horn.
The O gauge locos are among the best running locomotives Lionel made in the postwar period. Only the FM TrainMasters will out pull a double motored F3.
The Santa Fe is the most common of the Lionel F3 locos. Collectors will pay a premium for really clean locos, and also will pay hundreds of dollars for the separate box that holds an AA or AB pair.