Development was led by OKB-1 (S. P. Korolev),[1] and a total of nine flight tests were carried out, of which the two first failed, with the last launch taking place in June 1963.[2] Two versions of the RT-1 were developed, with the first failing its first flight, but succeeding in its second in 1961. A second version was tested in 1965 with three flights, of which two failed. The RT-1 program was cancelled before any service.[citation needed]