Northrop Delta  The Northrop Delta was an American single-engined passenger transport aircraft of the 1930s. Closely related to Northrop's Gamma mail plane, 13 were produced by the Northrop Corporation, followed by 19 aircraft built under license by Canadian Vickers Limited. When Jack Northrop set up the Northrop Corporation as a joint venture with the Douglas Aircraft Company in 1932, he set out to design two closely related single-engined aircraft as the new company's first products: a mailplane/record-breaking aircraft, which was designated the Gamma, and a passenger transport, the Delta. The Delta was a low-winged monoplane, with a fixed tailwheel undercarriage. It was of all-metal, stressed-skin construction, with streamlining spats covering the main landing gear. While the Delta's wings were common with those of the Gamma, it had a new, wider fuselage, which seated the pilot in an enclosed cockpit immediately behind the engine, and had accommodation for eight passengers in a cabin behind the pilot. The first Delta was flown in May 1933, and received an airworthiness certificate in August that year. Although it was intended that the Delta would be sold in both airliner and executive transport (initially named "Victoria") versions, a change to the regulations governing commercial air transport in the United States in October 1934, prohibiting the use of single-engined aircraft to carry passengers at night or over rough terrain which would prevent a forced landing, stopped the market for single-engined airliners in the United States, and only three aircraft, all ordered before the passing of this regulation, were built as airliners. These consisted of the prototype, leased to Trans World Airlines for use to carry airmail, which crashed on 10 November 1933, one sold to Pan-Am for use by its Mexican subsidiary, destroyed by a fire in May 1934 and one sold to AB Aerotransport of Sweden, delivered in April 1934. AB Aerotransport purchased a second Delta, but this was a dedicated mailplane which more closely resembled the Gamma, with a slim fuselage carrying its cargo in a compartment ahead of the cockpit. A single aircraft was built for the United States Coast Guard. Designated the Northrop RT-1, this was used as the personal transport of Henry Morgenthau, Jr., the Secretary of the Treasury and as a staff transport. Seven more aircraft were built as executive transports for private owners. Of these, three were purchased by the Spanish Republicans for use in the Spanish Civil War.