T. Claude Ryan was the founder of the Ryan Aeronautical Company, the second incarnation of a company with this name, and the fourth company with which he had been involved to bear his name (the first, Ryan Airlines, was the manufacturer of the Ryan NYP, more famously known as the
Spirit of St. Louis). He began the development of the
ST (for "Sport Trainer", and also known as S-T), the first design of the company, in 1933. The ST featured two open
cockpits in
tandem in a
semi-monocoque metal
fuselage of two main frames – one steel, the other half of steel and half of aluminium alloy (
alclad) – to take the loads from the
wing spars and six more alclad frames; and alclad skin. The fuselage only required eight
bulkheads, and no longerons or stringers were required. According to Cassagneres, "The stressed skin, of heavy 18 and 20 gauge 24ST Alclad, was riveted to the
drop-hammer formed
dural bulkhead rings." The main fuselage bulkhead, "was of built-up welded sheet steel and carried the important spar fittings as well as attachment points for the diagonal wing bracing strut, the upper landing wires, and lower flying wires." Cassagneres goes on to state, "The wings were constructed of solid spruce spars, stamped aluminum alloy ribs, and steel compression members, and were fabric covered. Ailerons and flaps were steel and aluminum structure with fabric covering. All tail surfaces were constructed entirely of tubular aluminum alloy with stamped ribs, and fabric covered." Five STs were built, each powered with a 95HP Menasco B4 engine before the follow-on
ST-A (A for
Aerobatic) was developed with a more powerful 125HP Menasco C4 engine. A single
ST-B was produced, this being an ST-A with only one seat and an extra fuel tank where the front cockpit normally was; this aircraft was subsequently converted back to ST-A standard. The ST-A was further developed as the
ST-A Special, with a super-charged 150HP Menasco C4-S engine of increased power. In 1937 the ST-A Special was developed into a military version, the
STM (also ST-M) series. The first STMs were virtually identical to the STA-Special. The STM-2 was derived from the STM with changes including wider cockpits to enable military pilots to enter and exit while wearing
parachutes, external stringers, and provision for a machine gun on some examples. After the ST-M came the
ST-3, a substantial redesign in 1941 partly brought about by the unreliability of the
Menasco engines fitted to STs to that point. The
United States Army Air Corps (USAAC) had purchased several dozen ST-M variants under various designations and had Ryan Aeronautical re-engine most with
Kinner R-440 radial engines. The ST-3 gave rise to another model developed in 1941 and early 1942, this was the
ST-3KR (for
Kinner
Radial). The ST-3KR had a more powerful
Kinner R-5 engine fitted and became the definitive model; more than 1,000 military versions were built during
World War II as
PT-22 Recruits. The first Ryan ST flew for the first time on 8 June 1934 Another 1,253 military versions were produced in 1942 and 1943, for a total of 1,568 aircraft of all models. ==Operational history==