The ALCO DL-109 was one of six models of A1A-A1A Diesel locomotives built to haul passenger trains by the American Locomotive Company (ALCO) between December, 1939 and April, 1945 ("DL" stands for Diesel Locomotive). They were of a cab unit design, and both cab-equipped lead A units DL-103b, DL-105, DL-107, DL-109 and cabless booster B units DL-108, DL-110 models were built. The units were styled by noted industrial designer Otto Kuhler, who incorporated into his characteristic cab (US Patent D121,219) the trademark three-piece windshield design. A total of 74 cab units and four cabless booster units were built. History All models developed . The first unit built as ALCO Specification DL-103b was longer than the other cab units, and became Chicago, Rock Island and Pacific Railroad #624. The DL-103b had the two radiator sections positioned together at the end of the carbody, while all other units had a split radiator arrangement with one placed at the back of the unit and one situated in the middle. The DL-103b was built with twin 6-cylinder ALCO 538T diesel engines as prime movers; all other DLs in this series were built with the newer twin 6-cylinder ALCO 539T diesel engines. The DL-103b also had all-electric driven accessories, while the later models had belt-driven accessories. The differences between all subsequent models were minor. The DL-105s went to the Rock Island as #622 and GM&O #270-271. All other early customers got DL-107 cab units and DL-108 boosters until the first DL-109 was delivered to the New Haven. During the war, the Gulf, Mobile & Ohio and Southern Railway bought DL109s and the Southern bought the only DL-110. It is not known whether this is because the model was a significant improvement, was the model approved for wartime production, or both. The New York, New Haven and Hartford Railroad received special permission from the War Production Board to purchase #0710–#0759 as dual-use (passenger/freight) locomotives; they were built between 1942 and 1945. Passenger-only locomotives (including the rival EMD E6) were not approved for production until early 1945. The first ten, numbers 0700 through 0709, were delivered starting right after the attack on Pearl Harbor in December 1941 from ALCO's Schenectady factory, allowing the road to prove their freight-hauling abilities just in time. The New Haven owned the most DL-109s, rostering 60 units (of the 62 built) in 1945. The New Haven DL-109s could be found hauling passenger