The Martin B-26 Marauder was one of the most controversial American combat aircraft of the Second World War. It was primarily used in Europe, and was in fact numerically the most important USAAF medium bomber used in that theatre of action. However, on four occasions, investigation boards had met to decide if the development and production of the Marauder should continue. The Marauder survived all attempts to remove it from service, and by 1944, the B-26s of the US 9th Air Force had the lowest loss rate on operational missions of any American aircraft in the European theatre, reaching a point less than one half of one percent.
Despite its high landing speed of 130 mph, which remained essentially unchanged throughout the entire production career of the B-26 in spite of numerous modifications made to reduce it, the Marauder had no really vicious flying characteristics and its single-engine performance was actually fairly good. Although at one time the B-26 was considered so dangerous an aircraft that aircrews tried to avoid getting assigned to Marauder-equipped units and civilian ferry crews actually refused to fly B-26s, it turned out that the Marauder could be safely flown if crews were adequately trained and knew what they were doing. It nevertheless did demand somewhat of a higher standard of training from its crews than did its stablemate, the B-25 Mitchell. However, once mastered, the B-26 offered a level of operational immunity to its crews unmatched by any other aircraft in its class.
A total of 5157 B-26 Marauders were built. Although on paper the B-26 was a more advanced aircraft than its stablemate, the North American B-25 Mitchell, it was built in much fewer numbers because it was more expensive to manufacture and had a higher accident rate.
One of the most commonly-asked questions is the difference between the Martin B-26 Marauder and the Douglas B-26 Invader. They were two completely different aircraft and had been designed to completely different requirements. The Douglas B-26 Invader had been originally been designated A-26, and was a twin-engined attack bomber intended as a successor to the Douglas A-20 Havoc. In 1948, the newly-independent Air Force decided to eliminate the A-for-Attack series letter as a separate designation, and the A-26 Invader was redesignated B-26, in the bomber series. There was no danger of confusion with the Martin B-26 Marauder, since this aircraft was by that time no longer in service with the US Air Force.
The history of the Martin Marauder dates back to early 1939. Both the North American B-25 Mitchell and the Martin B-26 Marauder owe their origin to the same Army Air Corps specification. On March 11, 1939, the Air Corps issued Proposal No. 39-640 for the design of a new medium bomber. According to the requirements listed in the specification, a bombload of 3000 pounds was to be carried over a range of 2000 miles at a top speed of over 300 mph and at a service ceiling exceeding 20,000 feet. The crew was to be five and armament was to consist of four 0.30-inch machine guns. The proposal called for either the Pratt & Whitney R-2800, the Wright R-2600, or the Wright R-3350 radial engine.
Requests for proposals were widely circulated throughout the industry. Proposals were received from Martin, Douglas, Stearman, and North American. The proposal of the Glenn L. Martin company of Middle River, Maryland (near Baltimore) was assigned the company designation of Model 179. Martin assigned 26-year old aeronautical engineer Peyton M. Magruder as Project Engineer for the Model 179. Magruder and his team chose a low-drag profile fuselage with a circular cross section. Since the Army wanted a high maximum speed but hadn't specified any limitation on landing speed, the team selected a high-mounted wing with a wingspan of only 65 feet. Its small area gave a wing loading of more than 50 pounds per square foot. The wing was shoulder-mounted to leave the central fuselage free for bomb stowage. The wings were unusual in possessing no fillets. The engines were to be a pair of 1850 hp Pratt & Whitney R-2800-5 Double Wasp air-cooled radials, which were the most powerful engines available at the time. Two-speed mechanical superchargers were installed in order to maintain engine power up to medium altitudes, and ejector exhausts vented on each side of the closely-cowled nacelles. The engines drove four-bladed 13 foot 6 inch Curtiss Electric propellers. Large spinners were fitted to the propellers, and root cuffs were added to aid in engine cooling.
The armament included a flexible 0.30-inch machine gun installed in the tip of a transparent nose cone and operated by the bombardier. Two 0.50-inch machine guns were installed in a Martin-designed dorsal turret located behind the bomb bay just ahead of the tail. This was the first power-operated turret to be fitted to an American bomber. Another 0.30-inch flexible machine gun was installed in a manually-operated tunnel position cut into the lower rear fuselage. There was a 0.50-inch manually-operated machine gun installed in a pointed tailcone. The tail gunner had enough room to sit in an upright position, unlike the prone position that had been provided in the early B-25.
There were two bomb bays, fore and aft. The bomb bay doors were unusual in being split in tandem, the forward pair folding in half when opened and the aft set being hinged normally to open outward. Two 2000-lb bombs could be carried in the main bomb bay, but up to 4800 pounds of smaller bombs could be carried if the aft bay was used as well.
Detailed design of the Model 179 was completed by June of 1939. On July 5, 1939, the Model 179 was submitted to a Wright Field Board. The Martin design was rated the highest of those submitted, and on August 10, 1939, the Army issued a contract for 201 Model 179s under the designation B-26. This contract was finally approved on September 10. At the same time, the competing North American NA-62 was issued a contract for 184 examples under the designation B-25. Since the design had been ordered "off the drawing board", there was no XB-26 as such.
Although the first B-26 had yet to fly, orders for 139 B-26As with self-sealing tanks and armor were issued on September 16. Further orders for 719 B-26Bs on September 28, 1940 brought the total B-26 order to 1131 aircraft.
Early wind tunnel test models of the B-26 had featured a twin tail, which designers thought would provide better aerodynamic control. This was dropped in favor of a single fin and rudder so that the tail gunner would have a better field of view.
The B-26 had a semi-monocoque aluminum alloy fuselage fabricated in three sections. The fuselage had four main longerons, transverse circular frames, and longitudinal stringers covered by a metal skin. The mid section with the bomb bays was built integrally with the wing section. The retractable tricycle landing gear was hydraulically actuated. The nosewheel pivoted 90 degrees to retract into the nose section, and the mainwheels folded backwards into the engine nacelles. The tail fins were of smooth stressed skin cantilever structure. The elevators were covered with metal skin, but the rudder was fabric covered.
The first B-26 (c/n 1226, USAAF serial 40-1361) took off on its maiden flight on November 25, 1940, with chief engineer and test pilot William K. Ebel at the controls. The first B-26 initially flew without any armament fitted.
The first 113 hours of flight testing went fairly well, and there were few modifications needed. However, a slight rudder overbalance required that the direction of travel of the trim tabs be reversed.
Since there was no prototype, the first few production aircraft were used for test purposes. On February 22, 1941, the first four B-26s were accepted by the USAAF. The first to use the B-26 was the 22nd Bombardment Group (Medium) based at Langley Field, Virginia, which had previously operated Douglas B-18s.
A series of failures of the front wheel strut resulted in a delay in bringing the B-26 to full operational status. Although the forward landing gear strut was strengthened in an attempt to correct this problem, the true cause was an improper weight distribution. The manufacturer had been forced to deliver the first few B-26s without guns, and had trimmed them for delivery flights by carefully loading service tools and spare parts as ballast. When the Army took the planes over, they removed the ballast without replacement and the resultant forward movement of the center of gravity had multiplied the loads on the nosewheel, causing the accidents. The installations of the guns corrected the problem.
It turned out that the earliest nose gear collapses were of diverse scenarios and were not necessarily solved by solving the c.g. problem. Prior to solution of the c.g. problem, there were three nose gear collapses of record involving USAAC B-26s. In chronological order,: 40-1364 had its nose gear collapse while attempting takeoff from a possibly soft, rutted grass field at Patterson Field in the spring of 1941; 40-1365 had its nose gear collapse after landing, taxiing and stopping for another plane to pass, a possible cocked-too-far-to-the-side-nosewheel, and the pilot may have gunned the engines to resume taxiing, which is when the collapse occurred; 40-1372 had its nosewheel collapse as soon as it touched down, apparently on pavement, at Langley. The pilot stated that, "The landing seemed to be smooth," (aside from the nose gear collapse), suggesting that he did not let the nose gear slam the ground. However, we cannot rule out the possibility of a stall at the tail causing the nose to come down too quickly, but if so, that s uggests the pilot waited a bit too long to ease the nose gear down to the ground due to his lack of experience in the B-26.
Various ground crew reported at reunions that the locking mechanism at the top of the nose gear strut could be defeated by bumps or slams. There was a theory about metal fatigue, but maybe only Martin could speak to that. Col. Maiersperger recalled that the caster angle of the first nose gear struts was quickly revised to improve roll characteristics and Martin strengthened the strut.
A modest number of nose gear collapses continued after the c.g. problem was solved, and some of them were likely pilot error, including 40-1462 three months after the c.g. problem was identified. There were apparently one or more design defects, and possibly one or more manufacturing defects, in the nose gear of the early planes. Bernard Mallon, another B-26 researcher, also points to a defect in the assembly. Martin addressed at least some of those defects, but their remedies may have escaped the attention of enthusiasts.
Solving the c.g. problem, according to Col. Maiersperger, allowed pilots to fix problems with the landing flare and greatly reduced the number of hard landings, several of which had seriously damaged the main landing gear.
The last B-26 was delivered in October of 1941. That month, the Martin Middle River production line shifted over to the B-26A version.
40-1361/1561 Martin B-26 Marauder
Engines: Two Pratt & Whitney R-2800-5 Double Wasp air cooled radial engines, rated at 1850 hp each. Performance: Maximum speed 315 mph at 15,000 feet. Cruising speed 265 mph. An altitude of 15,000 feet could be attained in 12.5 minutes. Service ceiling 25,000 feet. Range was 1000 miles at 265 mph with a 3000-pound bombload. Weights: 21,375 pounds empty, 32,025 pounds gross. Dimensions: Wingspan 65 feet 0 inches, length 56 feet 0 inches, height 19 feet 10 inches, wing area 602 square feet. Armament: One flexible 0.30-inch machine gun installed in the tip of a transparent nose cone and operated by the bombardier. Two 0.50-inch machine guns in a Martin-designed dorsal turret located behind the bomb bay just ahead of the tail. One 0.30-inch flexible machine gun was installed in a tunnel position in the lower rear fuselage. One flexible 0.50-inch machine installed in a tail position. The maximum bombload was 5800 pounds.