N1-L3 was underfunded and rushed, starting development in October 1965, almost four years after the Saturn V. The project was badly derailed by the death of its chief designer Sergei Korolev in 1966. Each of the four attempts to launch an N1 failed, with the second attempt resulting in the vehicle crashing back onto its launch pad shortly after liftoff and causing one of the largest artificial non-nuclear explosions in human history. The N1 program was suspended in 1974, and officially canceled in 1976. All details of the Soviet crewed lunar programs were kept secret until the Soviet Union was nearing collapse in 1989.