The NASA Crawler-Transporters were designed to transport Saturn V rockets on their mobile launch platforms between the Vehicle Assembly Building and the launch pads at the Kennedy Space Center in Florida. They also moved the Mobile Service Structure from its parking place to the launch pad for pre-flight preparations, then back prior to launch. During the Shuttle era, they transported the mobile launcher and Shuttle, but the service structure was fixed at the pad. The Space Launch System (SLS) uses the mobile launcher with an umbilical tower but no separate service structure. When in operation, the crawler burns 296 litres of diesel fuel per kilometre, which works out to U.S.-style fuel economy of 0.008 miles per gallon.
When delivered in 1965, the Crawler-Transporter was the largest self-powered land vehicle in the world, 40 by 30 metres in size and weighing 2,721 tonnes. It held this record for 48 years until 2013, when XCMG XGC88000 crawler crane became the new champion, at 173 metres total length and mass of 5,350 tonnes.
Only one of the two crawlers is presently in service for SLS. NASA has offered the other for lease to private space companies but has found no takers to date.