Under 5 days — about 4 days and 15 hours
That record belongs to the SS Robert E. Peary, assembled in 4 days, 15 hours, and 29 minutes in November 1942 as a publicity stunt using prefabricated, welded sections. It was a one-off feat, not the norm: most Liberty Ships took far longer, with the average build time falling to roughly 42 days by 1943. Even so, U.S. shipyards launched about three ships a day at peak and turned out 2,710 in under four years — a pace Axis industries could not match.
