For decades NASA has used ex-military M-113 tracked armored personnel carriers as regular and emergency transports at launch sites. In the event of a possible explosion while the crew of a manned rocket were already onboard, the M-113s were used to provide speed and protection as the astronauts sped away from the unstable rocket. The M-113s are getting old and need to be replaced. NASA planners did the math and realized that the many surplus MRAP (Mine Resistant Ambush Protected) trucks were cheaper than another tracked armored vehicle and offered better protection from the blast produced by a launcher exploding on the ground. The U.S. military was giving many surplus MRAPs away to other government agencies and that was an attractive price. NASA obtained four Caiman 6x6 MRAPs and modified them as astronaut carriers. Starting in 2007 the Department of Defense bought 1,700 Caiman 6x6 MRAPs and most of these have been retired.
The M-113 weighed 12 tons and had a top speed of 65 kilometers an hour. The Caiman 6x6 MRAPs are heavier (18 tons) and have a V shaped underbody that deflects the force of an explosion. The pressurized passenger cabin also keeps out blast effect, as well as a lot of the noise. This unique South African design has greatly reduced the effectiveness of roadside bombs and improvements were made since these vehicles served in Iraq and Afghanistan, including more anti-shock protection inside the crew compartment and improved ability to keep passengers alive when the vehicle was hit with a large blast shockwave. An MRAP, being a wheeled vehicle, can move nearly twice as fast on a flat surface as an M-113. MRAPs are also easier to learn how to drive and cheaper to maintain. MRAPs are also more comfortable to ride in and are regularly used to transport astronauts to their launch rocket.