This fourth and final volume of the Apollo Spacecraft Chronology covers a period of eight and a half years, from January 21, 1966, through July 13, 1974. The events that took place during that period included all flight tests of the Apollo spacecraft, as well as the last five Gemini flights, the AS-204 accident, the AS-204 Review Board activities, the Apollo Block II Redefinition Tasks, the manned Apollo flight program and its results, as well as further use of the Apollo spacecraft in the Skylab missions. The manned flights of Apollo, scheduled to begin in early 1967, were delayed by the tragic accident that occurred on January 27, 1967, during a simulated countdown for mission AS-204. A fire inside the command module resulted in the deaths of the three prime crew astronauts, Virgil I. Grissom, Edward H. White II, and Roger B. Chaffee. On January 28, 1967, the Apollo 204 Review Board was established to investigate the accident. It was determined that action should be initiated to reduce the crew risk by eliminating unnecessary hazardous conditions that would imperil future operations. Therefore, on April 27, a NASA Task Team-Block II Redefinition, CSM-was established to provide input on detailed design, overall quality and reliability, test and checkout, baseline specification, configuration control, and schedules.