11/30/2012. Remarks by Johan Visschedijk: "The USAF ordered On Mark Engineering Company of Van Nuys, California – a firm experienced in the modification and remanufacture of B-26s for use as executive aircraft – a prototype of a rebuilt B-26 for use in the counter-insurgency role.

On Mark made the following modifications: substitution of 2,500 hp Pratt & Whitney R-2800-103W radial engines; use of fully reversible, automatic feathering propellers; strengthened wings with steel straps on top and bottom of the spars; use of an enlarged rudder to improve single-engined handling; installation of permanent 165 gal (625 l) wing tip tanks; use of anti-skid braking system, deicer boots and anti-icing devices; modernization of the instrument panel and installation of new electronic equipment; and provision for dual controls.

The dorsal and ventral turrets were eliminated and fixed armament consisted of eight 0.50 in (12.7 mm) machine guns in the nose. Alternatively, a glazed nose enabled the aircraft to be used for photographic reconnaissance. In addition, the aircraft was to be fitted with eight new wing pylons accommodating a variety of external stores.

The pictured prototype was originally built by Douglas at Tulsa, Oklahoma, for the USAAF under s/n 44-35634 as an A-26C-40-DT Invader, it was redesignated B-26C in 1948, while in 1962 it had been converted to a B-26B. Modification of the aircraft – redesignated YB-26K, renamed Counter Invader – was started in October 1962, and made its first flight on January 28, 1963, whereafter it was fitted with the guns and other equipment. Following extensive evaluation testing at Eglin, in October 1963 the USAF ordered forty B-26s modified to a standard closely matching that of the YB-26K.

The main difference between the prototype and production aircraft was the use of 2,500 hp R-2800-52W engines in place of the R-2800-103Ws. Bearing new serials 64-17640 to 64-17679, the B-26Ks were delivered to the USAF between June 1964 and April 1965, one of these, s/n 64-17670, was the YB-26K prototype brought up to B-26K standards. For foreign customers, notably Brazil, other contractors modified additional B-26s to standards approaching that of the B-26K; however, none of these aircraft officially received this designation.

In service with the USAF the Counter Invader was used by the 603rd Special Operations Squadron from Lockbourne AFB, Florida and Hurlburt AFB, Ohio in the operational training role and, more importantly, by the 606th Air Commando Squadron (later 609th Special Operations Squadron) from Nakhon Phanom Air Base in Thailand.

Whilst in Thailand the aircraft were redesignated A-26As since an agreement between the Thai and US Governments prohibited the basing of bombers in the former country (this restriction was later rescinded when B-52s were stationed at Thai bases), and the A-26As flew night interdiction missions over the Ho Chi Minh Trail until phased out of service in November 1969."

For more information on Douglas A/B-26 versions and conversions visit the dedicated website The Douglas A/B-26 Invader.