sandwiched layers of glass and polycarbonate vinyl, and prototype aluminum run-flat tires were added. Due to an increase of 25 percent more weight—to —the upgraded car received a hand-built V8 engine that provided a 17% increase in power, to . In 1967, the convertible was modified again with an upgraded air conditioning system, an openable rear-door window, and structural enhancement to the rear deck. Despite successive presidential state cars being built and delivered to the White House, the X-100 continued to be occasionally used by Presidents Lyndon B. Johnson, Richard Nixon, Gerald Ford, and Jimmy Carter until it was retired from service in early 1977. , it was publicly exhibited at The Henry Ford museum in Dearborn, Michigan. The license plates (DC plates, "GG-300") were removed from the X-100 when the vehicle was upgraded after the Kennedy shooting; when they were auctioned in 2015, they sold for . 1967 Lincoln Continental President Johnson preferred white convertibles, but "concerns for protocol and safety" had him receiving a black 1967 Lincoln Continental as his state car. The hardtop cost the Ford Motor Company about ; they in turn leased it to the federal government for per year. With of armor, "a bubble top thicker than the protective cockpit of an F-16 fighter", and a V8 engine, the car could still reach speeds of — or with four flat tires. This car also served Presidents Nixon, Ford, and Carter, and traveled to 32 nations before it was retired in the mid-to-late 1970s. In 1996, Ford restored the car to its original state and donated it to the Richard Nixon Presidential Library and Museum; the auto manufacturer chose Nixon's library because he took the car on several of his most-significant presidential trips. 1972 Lincoln Continental A modified, , 1972 Lincoln Continental was delivered to the White House in 1974. The six-passenger limousine was leased from the Ford Motor Company for per year and featured a , V8 engine. The fully loaded automobile also had external microphones to allow occupants to hear outside noises, full armor plate, bulletproof glass, and racks for the Secret Service to store submachine guns. The car was used by Presidents Nixon, Ford, Carter, Ronald Reagan, and George H. W. Bush. It was the vehicle in which Ford was shot at by Sara Jane Moore. During the March 1981 attempted assassination of Ronald Reagan, the car was hit by the last