Apollo 6
The Apollo 6 mission, which took place on April 4, 1968, was the last uncrewed Apollo flight. The success of the mission allowed the next Apollo mission, Apollo 7, to be launched with a crew.
The Apollo 6 Command Module (CM 020) was launched from Kennedy Space Center on April 4, 1968, and recovered in the Pacific Ocean 10 hours later. The mission was the second test flight for the giant Saturn V launch vehicle. An engineering test version of the lunar module, LTA-2R, was aboard to provide information on launch characteristics without having to use an actual lunar module. The Apollo 6 spacecraft itself performed well on the mission despite problems with the Saturn V's first, second and third stages. The problems were solved after the flight and the next mission to use the Saturn V, the Apollo 8 mission, was launched with a crew.
The Apollo 6 Command Module (CM 020), featured a Block II "unified hatch." Following the tragedy of Apollo 1, the unified hatch was designed to permit a more rapid escape in an emergency. In this version of the hatch, the pressure vessel and heat shield hatches are combined, whereas they were previously two separate components.