Source: Andrea Germanos

The so-called “doomsday plane”—an aircraft modified by the U.S. military to be operated as a mobile command post and protect the president and high-ranking officials in the event of a high-level disaster—went on a reportedly unusual four-hour flight Monday following a perceived nuclear threat by Russian President Vladimir Putin.

According to multiple news reports, citing military flight tracking websites, the modified Boeing 747, using the call sign GORDO15, made a round-trip flight from a U.S. Air Force base in Nebraska to Chicago.

While the aircraft engage in regular testing missions, Monday’s flight was unusual, iNews reported because the plane was accompanied by two Cobra Ball jets with the ability to track ballistic missile data.

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The over $200 million “doomsday plane” is part of a fleet of E-4 series aircraft which have been militarized from a Boeing 747-200B to function as the National Airborne Operations Center. The E-4s have been in use since the 1970s, and at least one of the planes is kept on alert at all times.

“The conduct of E-4B operations encompasses all phases of the threat spectrum,” according to an Air Force description of the aircraft.

According to Boeing, the aircraft has 13 external communications systems, are designed for missions lasting 72 hours, and include “hardness” features to protect against electromagnetic radiation and the effects of a nuclear blast.

A video posted in 2020 by U.S. Defense News showcases the plane:

An Air Force spokesperson told iNews that Monday’s flight was “a routine sortie” and “not a response to actions taking place elsewhere in the world.”

Monday’s flight, however, took place amid Russia’s ongoing invasion of Ukraine and just hours after Putin ordered his military’s nuclear forces on “special alert.”

The Pentagon this week also announced Wednesday that it’s postponed scheduled nuclear missile tests for this weekend in light of the ongoing conflict.

“This is not a step backward in our readiness,” said Pentagon press secretary John Kirby, “nor does it imply that we will necessarily cancel other routine activities to ensure a credible nuclear capability.”