Martin B33 Super Marauder plus bonus A20 Havoc, B34 Ventura and Curtiss XP71

In 1939, the USAAC issued a requirement for a new medium bomber which could operate at high-altitude to avoid attack from ground fire. Preliminary designs were submitted by Martin and North American. The Martin XB-33 was redesigned from the B-26 Marauder, and North American XB-28 was based from the B-25 Mitchell. In 1940, both designs were awarded prototype contracts. The full-scale development of the XB-33 was begun in late 1940, and as it progressed, the Martin engineers found that a two-engine aircraft would not be capable of achieving the performance required in the Army specification. It was decided to radically alter the original design by adding two more engines. The entire project was scaled up to the approximate size of the Boeing B-29. The Army was sufficiently impressed with the new design; the two prototypes were redesignated XB-33A and an order for 400 production B-33A Super Marauders was placed. In 1944, Martin was awarded a contract to assemble B-29s which were urgently needed to enter Pacific theater. As B-29s had top priority to use the inventory, the entire B-33A order was cancelled before the prototypes were completed.