The T-4 was the third and last design of the Thaden Metal Aircraft Company which had been formed by Herbert von Thaden, a former United States Army Signal Corps pilot and engineer, to work on developing the first American all-metal aircraft. The T-4 was a high-wing monoplane powered by a 3000NaN0 Wright Whirlwind radial engine. It had a fixed conventional landing gear with a tailwheel. Two aircraft were built.