 The USSR made no crewed flights during this period but continued to develop its Soyuz craft and secretly accepted Kennedy's implicit lunar challenge, designing Soyuz variants for lunar orbit and landing.They also attempted to develop the N1, a large, crewed Moon-capable launch vehicle similar to the US Saturn V.

As both nations rushed to get their new spacecraft flying with men, the intensity of the competition caught up to them in early 1967, when they suffered their first crew fatalities.On January 27, the entire crew of Apollo 1, "Gus" Grissom, Ed White, and Roger Chaffee, were killed by suffocation in a fire that swept through their cabin during a ground test approximately one month before their planned launch.