The Air Force’s nuclear missile corps faces new strains after dozens more officers were implicated in an investigation of cheating on missile-launch proficiency tests. The number implicated in the probe has roughly doubled from the original 34 officers, meaning that about 14 percent of all launch officers are now sidelined.

Officials on Tuesday said the number of officers implicated now approaches 70 — all at Malmstrom Air Force Base, Mont., which is responsible for 150 Minuteman 3 nuclear missiles, or one-third of the entire Minuteman 3 force.