
By 1966, NASA had made sending astronauts to space seem somewhat routine having launched several Gemini missions the year before. They would continue to launch missions in service of Project Gemini throughout 1966 as they began to conduct unnamed testing of Apollo hardware.
On February 26, 1966, a Saturn IB carried a block 1 Command/Service Module (CSM) for AS-201, the first flight of the Apollo spacecraft. The launch carried the CSM to an altitude of 492.1 kilometers (265.7 miles) before returning to Earth safely. An additional two unmanned missions (AS-202 and AS-203) were carried out over the next few months. Although AS-202 had suffered delays due to CSM production delays, all three missions were conducted without incident. With the completion of the third test, NASA was given the go-ahead to launch the first crewed mission, Apollo 1.
Director of Flight Crew Operations Deke Slayton selected Gus Grissom, Ed White and Donn F. Eisele for the maiden crewed flight of the Apollo porgramme. However, during weightlessness training aboard a KC-135 aircraft, Eisele dislocated his shoulder twice and required surgery to repair the damage. His spot aboard Apollo 1 would be taken by Roger B. Chaffee, a 31-year-old naval aviator, and aeronautical engineer.

In preparation for the launch, the crew began training with the spacecraft at North American Aviation. On January 27, 1967, the three men were sealed inside the spacecraft for a “plugs-out” test. The test would simulate the spacecraft being switched from pad-supplied power to internal power. The testing was plagued with mishaps from the start with communications issues only serving to make matters worse. At around 18:31 EST, the crew reported two jolts that were outside what was expected from wind, engine gimballing or equipment input. Seconds later shouts of “Fire” began to ring out followed quickly by an explosion. An electrical fire had ignited in the cabin and spread quickly in the oxygen-rich atmosphere.
As the fire spread through the cabin, it burned around the spacecraft’s hatch openings hampering efforts by rescue teams. It would be another six minutes before rescue personnel managed to extinguish the fire and force the hatch down into the spacecraft. The heat and smoke would hamper rescuers efforts for several more minutes by which time Grissom, White and Chaffee had all succumbed to asphyxiation.

Immediately after the incident, NASA convened a review board to ascertain what had caused the fire. The review board was made up of representatives from NASA, the Air Force, and North America Aviation. It was also overseen by both the House of Representatives and the Senate.
Following their investigation, the review board determined that various safety procedures had either not been implemented or had not been properly implemented. Additionally, it found that the vehicle itself had no way of detecting a fire in the cabin. The pure oxygen mix utilised in the cabin was also identified as a major safety risk and one of the primary contributors to the ultimate death of the crew. On the recommendations of the review board, NASA overhauled their safety procedures and discontinued the Block 1 spacecraft. The Block II spacecraft and spacesuit designs were also revised to remove all flammable material and fit fire detection equipment. Finally, the agency shifted from a pure oxygen mix in the cabin to a nitrogen/oxygen mix.
The Apollo 1 fire was a crushing blow to the programme and the impact of the loss of the crew was unimaginable. Although the crew of Apollo 1 are but a footnote in the story of the American moon missions, on this, the 49th anniversary of the Apollo 11 moon landing, we remember the three men that gave their lives so that others would not have to.
The Apollo 11 Story Part 4: The Road to the Moon