This is a spacecraft model.
From the Airfix website:
"In May 1973 Skylab was launched using a two-stage Saturn V, sometimes called a Saturn INT-21. It was the only launch not directly related to the Apollo lunar landing program. Three crews lived aboard Skylab from May 25, 1973 to February 8, 1974, with Skylab remaining in orbit until July 11, 1979."
This massive kit of the Skylab version of the awesome Saturn V rocket will stand 76cm tall when completed.