Staff Writer (Updated: 5/11/2016):
January of 1939 saw the United States Army Air Corps (USAAC) issue a new requirement for a long-range light-to-medium bomber of considerable speed with the capability to mount at least 2,000lbs of ordnance. The Glen L. Martin Company entered the competition with their B-26 Marauder (then known as the Glen L. Martin 179) design and successfully obtained an initial order for 200 B-26's without so much as a single prototype let alone pre-production aircraft. The considerably deteriorating situation in Europe and in the Pacific necessitated the need for speed in production of such a design and thusly the B-26 was put to the assembly lines in little time (covering just two years from paper to working model). Within 12 months, the first B-26 was ready and made her first flight on November 25th, 1940 while 1,131 B-26A and B-26B models were already delivered.
The B-26 design was driven by the simple factor of pure speed. This was accomplished by selecting rather large, powerful engines and incorporating a small wing area with high wing loading. This produced an airframe that surpassed the USAAC requirements and then some, but provided for an aircraft with deadly-fast take-off and landing speeds and generally poor handling at lower speeds. In fact, landing speeds were between 120 and 135 miles per hour increasing the chances of damage to the airframe or injuries and fatalities to the crew substantially. Speeds became such a concern that the aircraft soon earned the nickname of "Widowmaker" due to at least one speed-related accident early on. As such, special military boards met to decide the fate of the Marauder project as a whole, grounding the aircraft in April of 1941 and instituting a few modifications in an effort to keep the type flying. This resulted in a B-26 with an increased wing area and redesigned taller vertical tail fin. Additionally, the Martin-produced powered dorsal turret had yet to be installed on previous models, leading to an imbalance of weight across the airframe, adding to the instability of the aircraft at lower speeds (effectively producing a stall on arrival).
Initial B-26's were fitted with the Pratt & Whitney R-2800-5 radial engine of 1,850 horsepower and produced in a batch of 201 examples. These were followed by the B-26A model series featuring the Pratt & Whitney R-2800-9 or R-2800-39 series engines. A-models were also the first to offer provision for a single internally-held torpedo. In addition to other subtle changes, the B-26A also increased its fuel capacity and therefore endurance. B-26A model production totaled about 139 examples.
The B-26B fitted the Pratt & Whitney R-2800-41 and R-2800-43 radial engines of 2,000 horsepower. These appeared in May of 1942 as a generally improved B-26A. Featured included better armoring and armament with a widened wingspan (642nd production model onwards) and propellers sans the spinners found on A-models. Production of the type numbered some 1,883 examples. The B-model series was in fact broken down into subvariants categorizing various subtle differences in construction. The base B-26B featured twin tail guns instead of one with a ventral gun added. The B-26B-1 was a slightly more improved B-26B model. The B-26B-2 featured the Pratt & Whitney R-2800-41 radial engines. The B-26B-3 was fitted with larger carburetors intakes and Pratt & Whitney R-2800-43 radial engines. The B-26B-4 was nothing more than a slightly improved B-26B-3 model. B-26B-10 throuh B-26B-55 included a myriad of changes covering the wingspan increase, addition of outboard flaps, taller vertical tail fin, a power-operated tail gun, cockpit armor protection and an increase to defensive armament.
The B-26C model was fitted with the Pratt & Whitney R-2800-41 series 2,000 horsepower engines. Like the B-26B before it, the C-model had their wingspan increased by exactly six feet. This was intended to reduced the issue of wing load common in the early B-26 design but was generally negated due to the increase in the wing's weight overall. B-26C's, for all intents and purposes, were generally similar to the B-26B models though constructed at Martin's Omaha subsidiary plant. Production totaled 1,210 examples.
The B-26F was brought online with a new angled wing in an effort to improve performance, particularly during take-off. These were completed in a batch of 300 examples. The B-26G were generally similar to the F-models and produced between 893 and 950 examples (sources differ on the exact total), becoming the last production models of the B-26 Marauder.
Some Marauders were converted as target tugs for gunnery trainer and designated as the AT-23A and AT-23B models. There were later updated with designations of TB-26B and TB-26C respectively. TB-26B conversions totaled 208 while 375 TB-26Cs were known to exist. TB-26C's were later granted for use by the United States Navy as JM-1 models with these totaling 225 on loan.
The Marauder airframe was also designed as an new-build crew trainer in the form of 57 TB-26G's. Like the TB-26C trainers loaned to the USN, the TB-26G was also loaned out as 47 JM-2's.
Marauder's were also sent via Lend-Lease to Britain (as Marauder Mk I, Mk IA, Mk II and Mk III marks) while others made their way into the inventories of Free French Forces and the South African Air Force.