Nuke proof doomsday plane: why has Boeing 747 E-4B been spotted in the UK - and what is the Flying Pentagon?

As the conflict in Ukraine rages on, worldwide talk about the prospect of a Russia-triggered nuclear war is arguably as high as it’s ever been.

Russian officialscontinue to remind the world of the country’s powerful arsenal of weapons, and though many Western leaders have denounced the rhetoric as bluster and an attempt to shift attention away from war crimes being committed on Ukrainian soil, it’s still a worrying prospect for many people.

Adding fuel to the irradiated fire, a so-called “nuke proof” aircraft has been seen circling the skies above the UK in recent days.

The Nightwatch aircraft - glibly referred to as the “doomsday plane” by many - is accompanying Joe Biden on his trip to Europe.

But why is that, and does it mean anything significant?

Here is everything you need to know.

What is the ‘doomsday’ plane?

To give it its technical name, the aircraft is actually a Boeing E-4B Advanced Airborne Command Post (AACP), though it is sometimes also referred to as the “Flying Pentagon”.

It is a strategic command and control military aircraft operated by the United States Air Force, which serves as a survivable mobile command post in the event of emergencies and crises.

The massive aircraft has three decks, and can accommodate a crew of up to 112 people including flight and mission personnel, the largest crew of any aircraft in US Air Force history.

It can also - through in-air refuelling - theoretically stay airborne for a week in emergencies, although the longest test flight so far completed clocked in at around 35 hours.

Is it ‘nuke proof’?

While the plane is often mistakenly thought to be fully “shielded” against a nuclear blast, this is not strictly true.

Were the aircraft to be caught directly within an area under nuclear attack - or at least as close to a nuclear detonation to suffer the effects of the blast wave - it would likely be damaged beyond use.

However, the plane is shielded from the effects of nuclear electromagnetic pulse (EMP), a burst of electromagnetic radiation created by a nuclear explosion which can produce damaging current and voltage surges.

It is also thought the aircraft is protected against radiation, and could withstand the high temperatures inflicted by a nuclear blast.

The plane costs nearly $160,000 (£121,495) per hour for the Air Force to operate.

Why is the plane flying over the UK?

The sighting of the plane should be of no cause for concern.

When the US President travels outside of North America using Air Force One, an E-4B aircraft is routinely deployed to a second airport in the vicinity of the President's destination.

For instance, when President Barack Obama visited Honolulu, Hawaii, an E-4B was often stationed 200 miles away at Hilo International Airport on Hawaii Island.

This is simply in case of any emergency - nuclear or otherwise - that renders Air Force One unusable.

Since President Joe Biden has travelled to Brussels recently for an emergency summit with fellow Nato leaders, it’s conceivable that the “nuke proof” aircraft has been stationed in the UK as a precaution.

A 200-mile radius around Brussels would put a number of south-eastern English airports within range - like London City Airport and Gatwick - as well as US force-hosting airbases like RAF Mildenhall and RAF Lakenheath in north-west Suffolk.

It is believed that the aircraft was indeed heading for Mildenhall.

As Biden heads to Poland for the second portion of his Europe trip, the plane will likely be seen flying again as it repositions itself closer to the President’s destination.

Where has it been spotted?

The aircraft was first spotted by enthusiasts flying just south of Ireland, before making its way to the UK.

Sightings have been reported in many areas of southern England.

Should I be worried?

As mentioned, the sighting of the plane does not point to any escalation in the Ukraine conflict, nor does it suggest the world is any closer to nuclear war.

The plane is simply deployed as standard whenever the President makes trips outside of the US.

This is in case of emergency, whether that be a nuclear threat or simply a technical fault with Air Force One which renders it unusable.

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