Several planned missions of the Apollo crewed Moon landing program of the 1960s and 1970s were canceled for a variety of reasons, including changes in technical direction, the Apollo 1 fire, hardware delays, and budget limitations. After the landing by Apollo 12, Apollo 20, which would have been the final crewed mission to the Moon, was canceled to allow Skylab to launch as a "dry workshop" (assembled on the ground in an unused S-IVB Saturn IB second stage). The next two missions, Apollos 18 and 19, were later canceled after the Apollo 13 incident and further budget cuts. Two Skylab missions also ended up being canceled. Two complete Saturn Vs ended up going unused and are currently on display in the United States.