Joe Biden's 'doomsday plane' — which the president would use in the event of a nuclear war — was spotted flying over Wales

• Joe Biden's "doomsday plane" was spotted flying over Wales on Tuesday night.
• The E-4B "Nightwatch" is designed to withstand a nuclear blast.

President Biden's "doomsday" E-4B plane was spotted flying over Wales on Tuesday night ahead of his commemoration of the Good Friday Agreement in Northern Ireland.

The president's "doomsday plane" is a $223 million E-4B called "Nightwatch," which is capable of surviving a nuclear blast. Following a nuclear attack, the president, secretary of defense, and joint chiefs of staff would board E-4B. From there, they would be able to order nuclear strikes or execute emergency war orders from the "flying war room," Insider previously reported.

The E-4B plane was spotted on Tuesday night flying over Wales, according to NorthWalesLive. According to the outlet, it is typical of the plane to follow closely behind the president's Air Force One in the skies when he travels.

The majority of the E-4B's capabilities are classified, but the plane can carry 112 people, can fly for 12 hours straight without refueling, and can refuel in the sky, allowing it to fly for several days in a row, the United States Air Force previously told Insider. Flying the E-4B "Nightwatch" costs $159,529 per hour, which is the most expensive plane that the Air Force operates, according to the Air Force.

The plane's windows are equipped with a wired mesh similar to those on the inside of a microwave oven door that prevents radiation from entering the plane, according to the Air Force. The crew of the E-4B works 24-hour, 7-day shifts and sleep in a cabin above the conference room that chiefs of staff and the president would use to give war orders.

The back of the plane holds its communication center, where operators can communicate with almost anyone in the world, according to the Air Force.

"It's designed that, in the most austere environments, during or after a nuclear war, it survives and can communicate, from the most cutting-edge communications technology to old, antiquated communications technology," Scott McCandless, the plane's former director of operations previously told Insider.