Reporting has taken me to many strange places. The oddest is the National Airborne Operations Centre, the doomsday plane that carries American defence secretaries around the globe. A specialised version of a Boeing 747, known as an E 4- B , its white and blue hull is studded with odd bulges and domes, concealing the gadgets needed to run a nuclear war from the air. Over the years the plane – or to be precise, planes, as the US Air Force runs four of them, each nearly identical – has carried me to more than a dozen countries as a member of the small travelling press corps that accompanies the civilian head of the Pentagon overseas. Add together the flights I have taken on the E 4- B , some as long as 19 hours, and I have spent weeks of my life aboard, most of them in the windowless conference room used to house the press, fitted with banks of computers and secure telephones that military officers and political leaders would use in the event of a war.

Most of the aircraft is off-limits to us, though on long trips the press may be invited to the secretary’s cabin in the nose for off-the-record talks. This article is being tapped out on a plane which, built in 1975, is older than many of the crew. It has a distinctly retro, late-cold-war feel, from the secretary’s padded-leather swivel seats, which would not shame a Bond villain, to the military-issue urinals bolted on the walls of the bathrooms (these drain straight into the sky, to avoid filling up the septic tanks on long flights).

The strangest part of flying aboard the E 4- B is mid-air refuelling, made necessary by the plane’s great weight, thanks to its unusual kit and special shield to protect it from the electromagnetic pulse produced by a nuclear blast. During an aerial refuelling, up to four oil tankers fly in from American air bases around the world and rendezvous with the boss in quick succession. On long flights like this one, from South Korea to Joint Base Andrews, just outside Washington, DC , two aerial refuellings are needed, each lasting around an hour.

View from the cockpit A photograph the writer took on board E4-B

To watch a refuelling from the cockpit is to witness a fine metaphor for an ageing superpower. Putting jet fuel into a 40-year-old jumbo jet while aloft is a risky, highly skilled operation beyond the capacities of most nations on earth. It is also wildly expensive. With a crew of dozens, including its own security force, the plane is reputed to cost $250,000 an hour to run. It is so old that a military cargo plane follows it to each stop round the globe, as an emergency spare.

I just watched a night-time refuelling off the coast of Alaska. From the cockpit of the E 4- B, the world is reduced to banks of glowing orange analogue dials and clunky switches, and the dark sky visible through the windscreen. I am ushered into a jump seat, from where I am startled to see the grey fuselage of another large aircraft a few yards ahead, which then looms even closer. As the refuelling takes place, all I can see through the windscreen is the bulk of the KC -10 tanker, a military version of a DC -10 airliner. Lit a sort of greenish-grey by spotlights, and bearing two parallel lines of orange lights along its belly for orientation, the tanker is trailing a thick fuel boom, stabilised by winglets. When close enough, a thinner probe emerges from the boom, quivering like a stallion ready to cover a mare.

“Opening door, get ready for some noise,” says one of the pilots to his co-pilot, and the sound of rushing wind can be heard from an unseen fuel port, just below their line of vision. The coupling is slow and tentative and takes several tries. Once, the probe is almost home when it rapidly vanishes back upwards into its protective boom, as if stung. “Contact” says a pilot, as it finally clunks into place. Against all instinct – planes are not meant to touch in the sky – 60,000lbs of fuel will be delivered mid-air. Maintaining contact requires constant trimming and adjustment from the pilot, squinting upwards with tense concentration. Turbulence makes both planes buck in the dark sky, and as fuel flows into the E 4- B it grows heavier, obliging the pilot to nudge the throttle for speed.

With such large planes if a pilot waits to see the effect of an action, it will be too late. Everything must be done by feel, and at one moment the planes close abruptly, pushing the fuel probe into the red-painted zone that signals danger. “Where did that come from?” one pilot asks the other laconically, as the planes inch further apart again. As long minutes tick by, they speak sparingly, exchanging notes about the position of the other plane, their overall fuel load. “Makes me feel like an American” says one, unexpectedly. In the darkness over the Pacific, the remark makes perfect sense.