WASHINGTON — Two of the U.S. Military's E-4B planes — commonly called the "Doomsday Plane" — were damaged and knocked out of service recently in a tornado at Offutt Air Force Base in Nebraska, according to two U.S. military officials.

Then-Secretary of Defense Leon E. Panetta, at top of stairs, waves as he boards a U.S. Air Force E-4B National Airborne Operations Center aircraft at Joint Base Andrews, Md., Oct. 21, 2011. TSgt Jacob N. Bailey / OASD/PA

The E-4B is the military's National Airborne Operations Center and if there is a national emergency or attack, the plane would serve as the command and control hub for the president, secretary of defense and joint chiefs.

The planes were damaged on June 16, the officials said. The military has four E4-Bs in the fleet so now half of the fleet is not operational.

The officials said the mission can still be accomplished with the two aircraft grounded.

Eight other aircraft also were damaged in the tornado. Those RC-135 surveillance aircraft have been repaired and returned to duty.