What was special about the B-26 Invader rebuilt by On Mark Engineering (YB-26K)?

On Mark Engineering was a US aircraft remanufacturing company established in 1954 at Van Nuys airport (California). Its work on the Invader did not stop at the surface: the fuselage and tail were rebuilt, the rudder was replaced with a larger version and removable dual controls were fitted as standard equipment. The wing was reinforced with steel straps laid from tip to root.

On Mark's proposal called for Pratt & Whitney R-2800-103W engines of 2,500 hp with water injection, more powerful, with which the aim was to maintain the aircraft's maximum speed. Wingtip tanks of 165 gallons were added and the aircraft received a full package of updated onboard electronics. The armament included .50-calibre SUU-12 machine-gun pods and bombs of up to 1,000 lb.

On Mark converted a single B-26 into the YB-26K prototype, which first flew on 28 January 1963. Once the tests were passed, that same aircraft was reconfigured along with 39 other aircraft and, in November 1963, the company received a contract to bring forty B-26s to the new standard; in total forty B-26K Counter-Invaders were produced, designed for counterinsurgency missions with the US Air Force and later redesignated A-26A. The type entered combat with the 609th Special Operations Squadron from bases in Thailand. The presence there was not free of friction: the Thai government was unwilling to allow the Americans to operate bomber aircraft from its air bases.