The first B-26s to arrive in Southeast Asia were deployed to Takhli RTAFB , Thailand in December 1960. These unmarked aircraft, operated under the auspices of the U.S. CIA (Central Intelligence Agency), were soon augmented by an additional 16 aircraft, 12 B-26Bs and B-26Cs plus 4 RB-26Cs under Operation "Mill Pond". The mission of all of these aircraft was to assist the Royal Lao Government in fighting the Pathet Lao. The aircraft were subsequently operated in South Vietnam under Project "Farm Gate". The only other deployment of B-26 aircraft to Laos prior to the introduction of the B-26K/A-26A, was the deployment of two RB-26C aircraft, specifically modified for night reconnaissance, deployed to Laos between May and July 1962 under Project "Black Watch". These aircraft, initially drawn from Farm Gate stocks, were returned upon the end of these missions.

The aircraft from Laos participated in the early phase of the Vietnam War with the USAF, but with Vietnamese markings as part of Project "Farm Gate". Though Farm Gate operated B-26Bs, B-26Cs, and genuine RB-26Cs, many of these aircraft were operated under the designation RB-26C, though they were used in a combat capacity. During 1963, two RB-26C were sent to Clark AB in the Philippines for modifications, though not with night systems as with those modified for Black Watch. The two aircraft returned from Black Watch to Farm gate were subsequently given the designation RB-26L to distinguish them from other modified RB-26C, and were assigned to Project "Sweet Sue". Farm Gate's B-26s operated alongside the other primary strike aircraft of the time, the T-28 Trojan, before both aircraft types were finally replaced by the A-1 Skyraider. The B-26s were withdrawn from service in early 1964 after two accidents were attributed to wing spar failure.