From Joe Baugher:
Douglas XA-26 Invader
The Douglas A-26 (later B-26) Invader was the outstanding American twin-engine light bomber of the Second World War. Although it did not begin to reach combat units until the spring of 1944, it went on to provide outstanding service for the rest of the war in both the European and the Pacific theatres of action. The Invader remained in American service in substantial numbers after the war, and was a major participant in the Korean War and was even around to serve in both phases of the Vietnam conflict, first with French and then later with American units. Although the last Invaders were withdrawn from USAF service in 1972, Invaders remained in service with many smaller air forces for many years thereafter. Invaders participated in several small-scale conflicts during the 1950s and 1960s, and carried out numerous clandestine operations, including the abortive Bay of Pigs operation of 1961.
The A-26 Invader originally began as a private venture on the part of the Douglas plant at El Segundo, California. In the autumn of 1940, Douglas began a preliminary design study to develop a common successor to the Douglas A-20, Martin B-26, and North American B-25 bombers, none of which had yet entered service with the US Army Air Corps. The Bomber Branch of the Experimental Engineering Section at Wright Field, Ohio assisted in this effort by pointing out some of the deficiencies of the company’s DB-7 twin-engined attack bomber that they had evaluated–lack of crew interchangeability, insufficient defensive armament, inadequate offensive firepower, and excessively long landing and takeoff distances.
At the end of January 1941, a team led by Edward Heinemann and Robert Donovan had come up with a proposal for a new twin-engine attack aircraft that would satisfy these requirements. It had a broad general family resemblance to the A-20 Havoc which was just then entering service with the Army Air Forces. It featured a mid-mounted wing with a laminar flow airfoil and which was fitted with electrically operated double-slotted flaps. The aircraft was to be powered by a pair of 2000-hp Pratt & Whitney R-2800-77 air-cooled radials. The aircraft was to have a large internal bomb bay capable of carrying 4000 pounds of bombs or two torpedoes, and was to be fitted with external racks underneath the outer wings for additional ordnance. The defensive armament was to be provided by a pair of remotely-controlled dorsal and ventral turrets, each housing two 0.50-inch machine guns and operated by a gunner sitting in a separate compartment behind the bomb bay.
A decision was made that the aircraft would be built in two separate versions, a three-seat light bomber version with a transparent nose for a navigator/bombardier and a two-seat night-fighter version with a solid nose carrying heavy forward-firing armament and AI radar. The two versions were to be essentially identical except for their noses.
The mockup was inspected between April 11 and 22 of 1941, and on June 2 the War Department authorized the construction of two prototypes under the new designation A-26. The first aircraft was to be a three-seat attack bomber version with a transparent nose and was to be designated XA-26-DE. The second aircraft was to be a two-seat night fighter version designated XA-26A-DE. Three weeks later, the contract was amended to include a third prototype designated XA-26B-DE. It was to be a three seat ground attack aircraft with an unglazed nose housing a 75-mm cannon.
On February 28, 1941, Douglas proposed that 500 of these aircraft be built at the Santa Monica plant, with the first deliveries set to begin 20 months after contract approval. However, the Douglas bid of $142,250 per aircraft was considered excessively high by the Army’s Materiel Division, and negotiations between the manufacturer and the War Department delayed approval of the project until October 21, 1941. At that time, it was planned that the three prototypes would be built at the Navy-controlled El Segundo but with production aircraft being built at the USAAF-controlled Santa Monica plant. The USAAF later decided to switch production of the A-26 to new Douglas plants that had been built in Long Beach, California and in Tulsa, Oklahoma in order not to disrupt ongoing production of A-20s, C-47s and C-54s at the Santa Monica plant.
There were some delays in the A-26 project which can be traced to USAAF indecision about what they really wanted. The AAF was initially undecided about what kind of mix that they wanted between light bombers with transparent noses, ground attack planes with solid noses housing 75-mm or 37-mm cannon, and attack bombers with solid noses housing a battery of forward-firing machine guns. The Army initially said that it wanted a 75-mm nose cannon installed in all 500 aircraft on order, but shortly thereafter changed its mind and wanted Douglas to proceed with its transparent-nosed light bomber version (which was to be designated A-26C) while continuing to develop alternative armament for the A-26B ground attack version.
The lengthy delays and slipped schedules led to a lot of mutual recrimination and finger-pointing between Douglas and the War Department, with each party blaming the other for the problems. There were late deliveries of undercarriage struts, self-sealing tanks, turrets, and other government-furnished equipment items such as engines, propellers and generators. The company was criticized for not making strong enough efforts to enroll subcontractors and for not providing enough staff to support production engineering at the Tulsa plant. The War Department accused Douglas of not really wanting to build the A-26 and of diverting too much of its efforts to transport aircraft which would promise to have a greater postwar payoff. As a result of all the delays, the A-26 took 28 months to proceed from first flight to full-scale combat operations. However, once the production line got into full swing, Douglas went on to produce 2400 Invaders during the last 20 months of the war.
The first flight of the XA-26-DE (41-19504) took place on July 10, 1942, with test pilot Ben O. Howard at the controls. The aircraft was powered by two 2000 horsepower Pratt & Whitney R-2800-27 radials driving three-bladed propellers with large spinners. The crew was three–a pilot, a navigator/bomb-aimer (who normally sat on a jump seat to the right of the pilot but also had a position in the transparent nose), and a defensive gunner sitting in a separate transparent compartment behind the bomb bay. For the initial phase of flight testing, defensive armament was not fitted, with dummy dorsal and ventral turrets being mounted.
The performance and handling of the prototype were excellent, but there were some problems with engine cooling which led to some cowling changes and the removal of the propeller spinners on production aircraft. The armament eventually fitted was two forward-firing 0.50-inch machine guns mounted on the starboard side of the nose and two 0.50-inch machine guns in each of the remotely-controlled dorsal and ventral turrets which were operated by a gunner in position just aft of the wing trailing edge. The upper turret was normally operated by the gunner, but it could be locked into the forward, no-elevation position and fired by the pilot. 3000 pounds of ordnance could be carried in two fuselage bays and an additional 2000 pounds on four racks underneath the outer wing panels.
Serial of Douglas XA-26 Invader
Serial Number: 41-19504 Model: Douglas XA-26 Invader Construction Number 1004
Specification of Douglas XA-26 Invader:
Engines: Two Pratt & Whitney R-2800-27 air-cooled radials, each rated at 2000 hp. Performance: Maximum speed 370 mph at 17,000 feet. Cruising speed 284 mph. An altitude of 20,000 feet could be attained in 10.2 minutes. Landing speed 100 mph. Service ceiling 31,300 feet. Normal range 1800 miles with 3000 pounds of bombs, Maximum ferry range 2500 miles. Dimensions: Wingspan 70 feet 0 inches, length 51 feet 2 inches, height 18 feet 6 inches, wing area 540 square feet. Weights: 21,150 pounds empty, 26,700 pounds loaded, 31,000 pounds maximum. Armament: Two forward-firing 0.50-inch machine guns mounted on the starboard side of the nose. Two 0.50-inch machine guns in remotely-controlled dorsal turret. Two 0.50-inch machine guns in remotely-controlled ventral turret. An internal bomb load of 4000 pounds could be carried Maximum total bomb load of 6000 pounds.
- United States Military Aircraft Since 1909, Gordon Swanborough and Peter M. Bowers, Smithsonian Institution Press, 1989.
- McDonnell Douglas Aircraft Since 1920: Volume I, Rene J. Francillon, Naval Institute Press, 1988.
- American Combat Planes, Third Enlarged Edition, Ray Wagner, Doubleday, 1982.