Wikipedia
The crawler-transporters, formally known as the Missile Crawler Transporter Facilities, are a pair of tracked vehicles used to transport spacecraft from NASA's Vehicle Assembly Building (VAB) along the Crawlerway to Launch Complex 39. They were originally used to transport the Saturn IB and Saturn V rockets during the Apollo, Skylab and Apollo–Soyuz programs. They were then used to transport Space Shuttles from 1981 to 2011. The crawler-transporters carry vehicles on the Mobile Launcher Platform, and after each launch return to the pad to take the platform back to the VAB.
The two crawler-transporters were designed and built by Marion Power Shovel Company using components designed and built by Rockwell International at a cost of each. Upon its construction, the crawler-transporter became the largest self-powered land vehicle in the world. While other vehicles such as bucket-wheel excavators like Bagger 293, dragline excavators like Big Muskie and power shovels like The Captain are significantly larger, they are powered by external sources.
The two crawler-transporters were added to the National Register of Historic Places on January 21, 2000.