At 6:31 p.m. EST, during a preflight "plugs out" test for the first crewed Apollo flight, a flash fire swept through Command Module 012. Strapped inside were three veterans of the early space program: Lieutenant Colonel Virgil I. "Gus" Grissom, veteran of Mercury and Gemini; Lieutenant Colonel Edward H. White II, who had made America’s first spacewalk during Gemini 4; and Lieutenant Commander Roger B. Chaffee, preparing for his first flight. The fire, fed by a pure-oxygen atmosphere and combustible materials within the cabin, spread in seconds. The crew’s efforts to open the inward-opening hatch were overcome by heat and smoke. All three perished before rescue crews could reach them.