Unfortunately, these B-26s began to suffer frequent wing failures, forcing them out of service. Those that remained were provided with a strengthening wing strap along the bottom of the wing spars to prolong service life. The success of these modifications led the USAF to order a remanufactured version of the Invader from the On Mark Engineering Company of Van Nuys, California that would be specifically adapted to the counterinsurgency role. The On Mark company had not previously built any military aircraft, but they had been extensively involved in conversions of Invaders for civilian use. The designation B-26K was applied and the name Counter Invader was chosen.
The Counter Invader was powered by a pair of 2500 hp Pratt & Whitney R-2800-103W water-injected engines driving a set of fully-reversible automatic feathering propellers. The wings were entirely rebuilt and strengthened by the installation of steel straps on the top and bottom of the spars. The rudder was enlarged to improve single-engine handling. Permanent 165 US gallon wingtip fuel tanks were installed. An anti-skid wheel braking system was adopted. Deicer boots and anti-icing equipment was added. The instrument panel was revised and provision for dual controls was made. New electronic equipment was adopted. Eight new underwing pylons were added for a variety of external stores. The dorsal and ventral defensive turrets were eliminated, and fixed armament consisted of a set of eight 0.50-inch forward-firing machine guns in the nose. Alternatively, the aircraft could be fitted with a glazed nose for photographic reconnaissance.
The first modified Counter Invader was built from RB-26C 44-35634. It had been converted into a B-26B in August of 1961 and employed as a squadron "hack". This aircraft was transferred to On Mark in October of 1962. When the work was completed, the aircraft was redesignated YB-26K. Contrary to some published sources, it was NOT assigned the new serial number 63-5634--the number 35634 painted on the aircraft were simply the last 5 digits of its original serial number. It flew for the first time on January 28, 1963. It was delivered to the 1st Air Commando Wing at Hurlburt for evaluation in June of 1963.
Following the completion of test flights, the USAF ordered 40 B-26Ks modified to similar standards. Most of the aircraft selected for conversion were B-26Bs or TB-26Bs, with just two B-26Cs and a single JB-26C. They were assigned the new serial numbers 64-17640/17679. The B-26Ks differed from the YB-26K primarily in having 2500hp R-2800-52W engines in place of the R-2800-103Ws. The propeller spinners were omitted and the six wing guns were deleted. The B-26K could carry 4000 pounds of bombs internally, plus up to 8000 pounds on the underwing racks. Besides the fixed wingtip tanks, two 230-gallon drop tanks or a 675-gallon bay tank could be carried. These changes increased the maximum cruising speed from 240 to 265 knots, the combat radius from 210 to 500 nautical miles, and increased the armament load from 7500 to 12,000 pounds. There were significant improvements in rate of climb and service ceiling. However, the aircraft was somewhat less stable than the original B-26 and it was no longer possible to trim it for hands-off flight.
All B-26Ks were fitted with an eight-gun solid nose, but this could be replaced by a glazed B-26C-type nose in about four hours. The B-26K could be readily converted into a RB-26K reconnaissance aircraft by the installation of a glazed nose and a removable bomb bay system of four cameras and flash ejectors.
The first B-26K flew on May 26, 1964. The B-26Ks were delivered to the USAF between June 1964 and April 1965. They had originally been intended to replace the ageing B-26s operating in Vietnam with Farm Gate. However, these B-26s had been taken out of service prematurely due to wing spar fatigue, and had been replaced by A-1 Skyraiders. Consequently, the B-26K was no longer urgently needed in Southeast Asia, and the planes were kept in the USA for the time being. They first entered service with the 602nd Fighter Squadron (Composite) at Hurlburt AFB. The squadron was later renamed the 6th Fighter Squadron (Composite). The last seven were allocated to the 605th Air Commando Squadron at Howard AFB in the Panama Canal Zone.
The B-26Ks spent the first couple of years of their service on training units in the USA and in Central America. In mid-December of 1965, the B-26 training program moved from Hurlburt to England AFB in Louisiana and the Invader unit changed its name to the 603rd Fighter Squadron, soon to be changed to the 603rd Air Commando Squadron.
In the spring of 1966, it was decided to deploy B-26Ks to Southeast Asia in an attempt to stem the flow of war material down the Ho Chi Minh trail from North Vietnam via Laos. Since northeastern Thailand was much closer to the intended area of operations in southern Laos, the US Government obtained permission for the Invaders to be stationed there rather than in South Vietnam. However, during the mid-1960s, Thailand did not permit the basing of bombers on its territory, and so in May 1966 the aircraft were reassigned the old attack designation of A-26A, thus bringing the Invader full-circle.
The A-26As deployed to Southeast Asia were attached to the 606th Air Commando Squadron, based at Nakhon Phanom Air Base in Thailand. The mission of the 606th was known as Lucky Tiger. The A-26A unit was officially known as Detachment 1 of the 603rd Air Commando Squadron on six months' temporary duty in Thailand. The operations of the A-26As over Laos were highly "black" and the national insignia were painted out in order to maintain some sort of plausible deniability if something went wrong and one of them were forced down. The area of the Laotian panhandle along the North Vietnamese border became known as Steel Tiger, and it became the primary target of the A-26As.
Most of the A-26A combat missions over Laos were interdiction missions flown at night, the North Vietnamese antiaircraft defenses that were installed along the Ho Chi Minh Trail making it too dangerous to fly slow-moving aircraft such as the piston-engined A-26A over the area during the day. The primary targets were truck traffic along the Trail. Sometimes the A-26As were equipped with AN/PVS2 Starlight scopes for enhanced nighttime visibility. Most of the time they were equipped with solid noses, but a few missions were flown with glass noses. By December 1966, the A-26As had claimed a total of 99 trunks destroyed or damaged. At the end of December, the aircraft were reassigned to the 634th Combat Support Group at Nakhon Phanom. In April of 1967, the A-26As were officially transferred over to the 609th Air Commando Squadron, which was part of the newly-formed 56th Air Commando Wing.
The A-26A could carry a maximum of 8000 pounds underneath the wings plus 4000 pounds internally. However, the actual load carried on combat missions was usually somewhat less in order to gain maneuverability and to reduce stress loads. A typical underwing load was a pair of SUU-025 flare dispensers, two LAU-3A rocket pods, and four CBU-14 cluster bomb units. Later, the rockets and flares were often replaced by 500 lb BLU-23 or 750 lb BLU-37 finned napalm bombs. The M31 and M32 incendiary clusters could also be carried, as well as M34 and M35 incendiary bombs, M1A4 fragmentation clusters, M47 white phosphorus bombs, and CBU-24, -25, -29, and -49 cluster bomb units. General-purpose bombs such as the 250-lb MK-81, the 500-lb MK-82, and 750-lb M117 could also be carried.
In the summer of 1968, all Air Commando Wings were redesignated as Special Operations Units, and the 56th ACW became the 56th Special Operations Wing, with the 609th ACS becoming the 609th Special Operations Squadron.
The night interdiction tasks of the A-26A were gradually taken over by AC-130A and AC-130E gunships, and the Counter Invaders were phased out of active service by November of 1969. The losses had been fairly heavy, with no less than twelve out of the 30 that had served in Thailand at one time or another having been lost to enemy action. The 609th SOS was awarded the Presidential Unit Citation for extraordinary gallantry.
Following their withdrawal from service, most of the A-26As were immediately transferred to storage with the MASDC at Davis-Monthan. Five were handed over to the South Vietnam air force for use as instructional airframes. These were blown up at Nha Trang in March of 1975 as the North Vietnamese army was about to overwhelm the South. Several A-26As ended up in service with clandestine operations in the Congo. Ten were held in readiness just in case they might be needed again, and it was not until February of 1973 that the last A-26A was consigned to storage. Five of them ended up in museums in the USA and South Korea.
64-17640/17679 On Mark B-26K Counter Invader rebuilt from WW II A-26 Invaders
Engines: Two Pratt & Whitney R-2800-52W air-cooled radials, each rated at 2500
hp for takeoff and 1750 hp at 15,000 feet.
Performance: Maximum speed 323 mph at 15,000 feet, 291 mph at sea
level. Cruising speed 169 mph. Stalling speed 114 mph. Initial climb
rate 2050 feet per minute. An altitude of 10,000 feet could be
attained in 8.1 minutes. Service ceiling 28,600 feet. Combat radius
700 miles with 3518 pound bombload. Normal range 1480 miles, Maximum
ferry range 2700 miles.
Dimensions: Wingspan 71 feet 6 inches (over wingtip tanks), length 51
feet 7 3/16 inches, height 19 feet 0 inches, wing area 540 square
Weights: 25,130 pounds empty, 37,000 pounds loaded, 39,250 pounds
Armament: Eight forward-firing 0.50-inch machine guns in nose. Six
forward-firing 0.50-inch machine guns in the wings. An internal bomb
load of 4000 pounds could be carried Up to 8000 pounds could be
carried on the underwing pylons. Maximum total bomb load of 12,000