Two of the Pentagon's four specially reinforced 'Doomsday' planes, designed to withstand the heat from a nuclear blast, have been grounded after being damaged by a tornado.

The Air Force said Friday that two E4-B Boeing 747s were damaged when a tornado whipped through Nebraska's Offutt Air Force Base with little advance warning on June 16.

Built in the 1970s during the Cold War, the planes are essentially flying command centers that can refuel in the sky and are designed to remain airborne for days on end in times of crisis.

The two damaged 'Doomsday' planes were reportedly parked in hangars during the storm, but their tails were exposed to strong winds.

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The Air Force said Friday that two E4-B Boeing 747s were damaged when a tornado whipped through Nebraska's Offutt Air Force Base earlier this month (file photo)

Defense Secretary James Mattis briefs reporters aboard a E4-B in April. The 'Doomsday' planes transport the defense secretary and serve as flying command posts

The EF1 tornado that whipped through Offutt Air Force Base on June 16 came with little warning. Damage to facilities on the base is seen

Trees were ripped from their roots and buildings were damaged in the powerful tornado

Downed tree limbs from the tornado on Offutt Air Force Base are seen. The tornado also damaged two EF-Bs on the ground at the base

Built in the 1970s during the Cold War, the planes are essentially flying command centers that can refuel in the sky and are designed to remain airborne for days on end in times of crisis

The Air Force has four E4-Bs, which also shuttle the secretary of defense around the world.

'Two E-4B National Airborne Operations Center aircraft stationed at Offutt AFB received storm damage,' Air Force spokesman Colonel Pat Ryder said.

Not including the damage to aircraft, the tornado caused an estimated $7million to $10million in damage to the base facilities, 55th Wing spokesman Drew Nystrom told the Omaha World Herald.

Additionally, seven RC-135 reconnaissance planes suffered minor damage in the tornado and another needed an inspection.

The E-4B is a 747 that has been reinforced to protect against the electromagnetic pulse from a nuclear blast and is shielded from a thermal blast.

The planes, also called 'National Airborne Operation Centers' when they are in-flight, have special equipment and have the capability to communicate with anyone from anywhere in the world and support analysts and strategists on the flight.

Defense Secretary James Mattis (left on stairs) exits his E4-B in April. Two of the Pentagon's fleet of four E4-Bs were damaged by a tornado earlier this month

The planes have special equipment and have the capability to communicate with anyone from anywhere in the world and support analysts and strategists on the flight

The plane's conference room is seen. The Doomsday planes can operate with the largest crew of any aircraft in the US Air Force at 112 people, both flight and mission personnel

Communications gear inside a E4-B is seen. The jets can unspool miles of low-frequency antenna to maintain contact with nuclear subs and other assets in times of crisis

The blue-and-white jets can also unspool miles of low-frequency antenna to maintain contact with nuclear subs and other assets in times of crisis.

One of the planes is typically kept running at all times, with the engine running 24 hours a day at the Offutt base when the president is in the US. In the event of an emergency, the plane is ready to take off almost immediately.

It is unknown how the damage to the two planes at Offutt impacted that contingency planning, information which is tightly held for national security reasons.

However, other aircraft in the fleet are capable of fulfilling the role of airborne command centers in times of emergencies, according to experts.

The cost and timeline for repairing the two damaged E4-Bs is unknown.