The teardrop-shaped APOLLO command module, (shown above) the living quarters for the three-man crews, had a differenct shape from the conical-nosed GEMINI and MERCURY. The attached cylindrical service module contained supplies as well as the Service Propulsion System engine that placed the vehicle in and out of lunar orbit.
On January 27, 1967, just as the program was nearing readiness for its first manned flight, tragedy struck. A fire inside an APOLLO command module (Spacecraft 012 shown above was the CM which was destroyed by the fire.) took the lives of astronauts Virgil "Gus" Grissom, Edward White and Roger Chaffee, who were training inside it at the time. The fire resulted in delays and modifications to the spacecraft, but by October 1968, APOLLO 7 was ready to carry three astronauts into Earth orbit, where they checked out the command/service module (both had been tested in an unmanned mode during the November 1967 APOLLO 4 mission, which also was the first flight of the SATURN V). By December 1968, APOLLO 8 was ready to try for lunar orbit (on the SATURN V's third outing), and seven months later APOLLO 11 made the first lunar landing.
By the time the APOLLO program ended in 1972, astronauts had extended the range and scope of their lunar explorations. The final three missions were far more sophisticated than the first three, in large part because the astronauts carried a lunar rover that allowed them to roam miles from their base. APOLLO 11's Armstrong and Aldrin spent only two-and-a-half hours walking on the surface. On APOLLO 17 the Moon walks totaled 22 hours, and the astronauts spent three days "camped out" in the Moon's Taurus-Littrow valley.
After six lunar landings the APOLLO program came to a conclusion (APOLLO 18, 19, and 20 missions had been canceled in 1970 because of budget limitations), and with it ended the first wave of human exploration of the Moon.
(The above narrative is from SPACE FLIGHT THE FIRST 30 YEARS, NASA publication NP-150, December 1991, p. 12.)