Short answers, pulled from the story.
North American Aviation received the initial Apollo contract on the 28th of November 1961. This agreement established the foundation for developing the spacecraft components required for lunar missions.
A cabin fire erupted during a launch rehearsal test on the 27th of January 1967 causing the deaths of three astronauts named Gus Grissom Ed White and Roger Chaffee inside the Block I command module. Investigators found that the two-piece plug hatch used on Block I could not be opened quickly enough during an emergency leading to recommendations to terminate the crewed Block I phase entirely.
Nine units carried astronauts to the Moon between December 1968 and July 1972 as part of the Apollo program. A total of nineteen command and service modules launched into space throughout the Apollo era including uncrewed test vehicles and those used for Skylab operations.
The final flown unit docked with Soviet Soyuz 19 on the 15th of July 1975 for the Apollo-Soyuz Test Project. This mission marked the end of operational flights for the command and service module fleet before some spacecraft were moved to museums in Washington D.C. London Moscow and various U.S. cities.
Engineers replaced the two-piece plug hatch that doomed the Apollo 1 crew during their fatal fire with a one-piece quick-release outward opening hatch for Block II versions. Aluminized PET film layers gave Block II heat shields a shiny mirrored appearance absent on earlier models while Block II shields adopted rectangular shapes with slightly rounded corners at propellant tank sectors.