The Martin B-26B was the most numerous version of the Marauder. At first it differed from earlier versions in having more powerful engines and increased armament, but starting with the 642nd aircraft it was also given longer wings and larger tail fin in an attempt to make it easier for inexperienced pilots to fly. In all 1,883 B-26Bs were built, 641 with short wings and 1,242 with long wings. In addition another very 1,210 very similar B-26Cs were built at Martin's new factory in Omaha.
Production began with the basic B-26B. This saw the rear .50in gun replaced by a double mounting, and the amount of ammo increased from 400 rounds to 1,500. A tunnel gun was added (either .30in or .50in depending on the source). The propeller spinners were removed and fittings to carry a torpedo became standard.
This was followed by the B-26B-2, which was given the R-2800-41 engine, providing 2,000hp at take-off and 1,920 normally. This gave the Marauder a top speed of 317mph and reduced its take-off run. The dash-2 was visually identical to the basic B-26B.
The B-26B-3 introduced the R-2800-43 engine. This provided the same power as the -41, but had enlarged carburettor intakes that could take a tropical sand filter.
The B-26B-4 was given a longer nose wheel strut. This increased the angle of incidence of the wing and shortened the take-off run. The nose gun was moved from its original position above the centre of the nose to the tip of the bombardier's Plexiglas structure. This version was also produced for the RAF, although with the defensive guns of the B-26A. In RAF service it was known as the Marauder 1A.
The last B-4s had their single ventral gun removed and .50in waist guns added below and behind the dorsal turret, each with a sliding hatch to cover the space when the gun was not in use.
The B-26B-10 brought the biggest change to the design of the Marauder with the introduction of longer wings, increasing the span to 71ft and the area from 602 to 658sq feet, and a bigger vertical fin and rudder. The wings were also given a slight dihedral, and slotted flaps instead of the earlier split flaps. The new wing was introduced to make the aircraft easier for inexperienced pilots to fly, but also reduced the top speed by 35mph to 282mph. The dash-10 was also given four more fixed forward firing 0.50in gins, two on each side of the fuselage mounted below and just behind the pilot's position and an extra fixed forward firing 0.50in gun in the nose. Finally the waist guns were moved one fuselage frame back and the windows increased in size.
The bigger wing didn't actually reduce the wing loading of the aircraft. On the basic B-26 that had been 53.16lb/sq.ft. On the short-winged B-26B that had risen to 56.48lb and on the late long-winged version that rose again to 58.05lb/sq.ft. The big improvements in safety that came with the later B-26Bs clearly owed far more to experience, and demonstrated the problems of ordering a modern new aircraft straight off the drawing board.
The B-26B-20 saw the introduction of a new power-operated Martin-Bell tail turret which improved the protection offered to the rear gunner and reduced the length of the aircraft to 56ft 1in. External armour plating was also added alongside the cockpit.
Production then continued through a series of blocks that saw only minor changes, ending with two hundred B-26B-55s, which saw the fixed forward firing gun removed from the nose, reducing the total to eleven.
Engine: Two Pratt & Whitney R-2800-39 Double Wasp radial engines
Power: 1,850hp at sea level
Wing span: 65ft 0in
Length: 58ft 3in
Height: 19ft 10in
Max take-off weight: 34,000lb
Max Speed: 311mph at 14,500ft
Service Ceiling: 23,500ft
Combat Range: 1,150 miles