Activated at March Field, California in early 1941 as part of the prewar mobilization of the Army Air Corps. Equipped with B-18 Bolos and Lockheed Hudsons. Engaged in coastal patrols over Southern California, later over the San Francisco area.

Re-equipped with B-25 Medium bombers, deployed to Seventh Air Force in Hawaii during the late summer of 1942. Completed final training in Hawaii and moved to Tarawa in the Central Pacific in December 1943. Entered combat and attacked enemy installations, airfields, and shipping in the Marshall Islands in preparation for the invasion by US forces, and after February 1944 staged through captured fields on Eniwetok to attack shipping in the Caroline Islands.

In April 1944 moved to Makin where its missions were directed primarily against shipping and bypassed islands in the Marshalls and Carolines. Returned to Hawaii in October 1944 for training with rockets and new B-25’s. Moved to Okinawa, May–June 1945. Bombed airfields, railways, and harbor facilities on Kyushu until August 1945. Also flew some missions against airfields in China.

Moved to Manila in December 1945. Inactivated in the Philippines on January 27, 1946.

The tank destroyer battalion was a type of unit used by the United States Army during World War II. The unit was organized in one of two different forms—a towed battalion equipped with anti-tank guns, or a mechanized battalion equipped with armored self-propelled guns. The tank destroyer units were formed in response to the German use of massed formations of armored vehicles units early in WWII. The tank destroyer concept envisioned the battalions acting as independent units that would respond at high speed to large enemy tank attacks. In this role, they would be attached in groups or brigades to corps or armies. In practice, they were usually individually attached to infantry divisions. Over one hundred battalions were formed, of which more than half saw combat service. The force was disbanded shortly after the end of the war when the concept had been shown to be militarily unsound.

The 533d was constituted as the 533d Bombardment Squadron and activated as a part of the 381st Bombardment Group, Heavy on 3 November 1942, at Gowen Field, Idaho. Soon after, the 533d trained under II Bomber Command at Pyote Army Air Field, Texas, where the first two phases of unit training took place. The rest of the training was conducted at Pueblo Army Air Base, Colorado and in the simulations throughout the country. Received deployment orders for the European Theater of Operations in May 1943.