The 28th Squadron was organized in the Philippines 15 years before the attack on 8 December 1941 and for many years was the only Air Corps Units located in the Philippines. The 28th Squadron was originally stationed at Nichols Field, Manila, but was moved to Clark Field in 1939. The organization was not actually a part of any Group, but a lone bombardment squadron, part of the Philippine defense, just prior to the arrival of the 19th Group. The squadron was equipped with B-10's, and later B-18's, which towed targets for artillery practice of the guns of Corrigador, search lights practice, and had a general training program.

30th, 32nd, 93rd, 435th, 912th