The Martin XB-33 was the designation given to two different designs for high altitude bombers, neither of which entered production.
Martin’s first attempt to produce a pressurised high altitude bomber, the XB-27, had been rejected at the blueprint stage. Work on their next attempt, the XB-33, began in October 1940. While the XB-27 had been loosely based on the B-26 Marauder, the new design had more in common with the Martin PBM Mariner. This included the use of dihedral on the horizontal tail surfaces, with vertical tail surfaces that were attached to them at ninety degrees, and long narrow tapering wings with the radial engines carried in nacelles roughly level with the horizontal tails. The XB-33 had a tricycle landing gear. It was to be powered by two 2,200hp Wright R-3360 eighteen cylinder radial engines, and would have had a wing span of around 100ft, length of 71ft and height of 22ft 6in.
As work continued with the project, more and more features, and thus weight, were added to the design. Eventually it became clear that the twin engine XB-33 couldn’t satisfy the Air Corps requirements, and work moved onto a four engine version.
The four engine version of the aircraft was given the XB-33A designation, and was internally known as the Martin Model 190. It was to be powered by four Wright R-2600-15 Cyclone engines, each providing 1,800hp (the R-3360 was required for the B-29 Superfortress), each given a two stage General Electric CMC-3 turbo-supercharger. It had some features in common with the twin engine version, including the ‘V’ shaped tail and the high mounted wing. The four engines were carried in large nacelles, and the inner nacelles carried the main retractable wheels. It had a larger wing, with a length of 134ft, and would have been longer and higher than the earlier design.
The aircraft was armed with eight 0.5in calibre machine guns. These included nose, forward belly, upper rear and tail power turrets that would have been remotely controlled. It would have been able to carry 10,103lb of bombs.
The Air Corps was suitably impressed with the new design. Martin were given a contract to produce two prototypes, and this was then followed by a production order for four Martin B-33As. However this order came too late in the war for Martin. The USAAF already had the B-29 in service, and the Convair B-32 as a backup, and the B-33 ‘Super Marauder’ wasn’t needed. As a result the order was cancelled before the prototypes had been completed. They were both dismantled, and the project ended with no aircraft completed.
Engine: Four Wright R-2600-15 Cyclone engines
Length: 79ft 10in
Empty Weight: 64,948lb
Gross Weight: 97,917lb
Maximum Speed: 345mph
Climb rate: 1,135ft/ min
Range: 2,000 miles at 242mph
Guns: Eight 0.5in machine guns in nose, forward belly, upper rear and tail positions.
Bomb load: 10,130lb