The Ryan STs (for "Sport Trainer", and also known as S-T) were a series of two seat, low-wing monoplane aircraft built by the Ryan Aeronautical Company. They were used as sport aircraft, as well as trainers by flying schools and the military of several countries.
The first Ryan ST flew for the first time on 8 June 1934 and production began the following year, when nine aircraft were delivered. Production rates remained low for several years, at about one aircraft every two weeks. This changed in 1940 when deliveries to military forces began in earnest; production that year was just under three aircraft per week. Total production of civil and military aircraft prior to the entry of the United States into World War II amounted to 315. Another 1,253 military versions were produced in 1942 and 1943, for a total of 1,568 aircraft of all models.
Source: Wikipedia, "Ryan ST", available under the CC-BY-SA License.