Part of Wings of War — From Zeppelin to Sixth Generation, our series on the great turning points of military aviation.

Just after one o’clock in the morning on 25 July 1943, a German night-fighter controller sat staring at his radar screen as the British bombers came in toward Hamburg. He had done this many times. The system was good: a chain of radars would track each bomber, and he would vector his night-fighters and the flak guns onto them one by one. Then, all at once, his screen went mad. Where there had been a few clear blips, there were suddenly thousands — a blizzard of false echoes, far more “aircraft” than could possibly exist, swamping every screen along the coast.

The bombers were dropping Window: bundles of aluminium foil strips, cut to exactly the right length to throw back a radar echo, tipped out by the handful into the night sky. Each strip looked, to the radar, like a bomber. The entire German air-defence system — radars, night-fighters, flak, searchlights — was blinded in minutes, and the bomber stream flowed through to a city that would burn terribly in the nights that followed. It was the first time an electronic trick had switched off an enemy’s air defences wholesale. Electronic warfare had come of age.

The war of the beams

Electronic warfare was born almost the moment radar and radio became weapons. As early as 1940, German bombers navigated to British targets by following radio beams — until British scientists worked out how to bend and jam those beams, sending the bombers astray in what Winston Churchill called the “Wizard War.” The German bombers rode along a radio beam aimed at their target, like an invisible railway in the sky; a young British scientist named R. V. Jones worked out what was happening, and Britain learned to detect the beams and subtly bend them, so that crews bombed open fields believing they were over a city. Neither side could see the other’s weapon, and yet the contest was as real as any dogfight. The principle revealed then has governed air combat ever since: any device that senses or signals can itself be detected, deceived or drowned out. Build a better radar, and you invite a better way to blind it.

Blinding the radar

The Window strips dropped over Hamburg were the simplest possible countermeasure — just foil cut to the radar’s wavelength — and yet they paralysed one of the best air-defence systems in the world. Both sides had actually discovered the trick and each had hesitated to use it, fearing the enemy would copy it. The British used it first, and to devastating effect. From that night onward, no air force could assume its radar picture was real, and the jamming of enemy sensors became a permanent part of every air campaign.

Into the missile age

The arrival of the radar-guided surface-to-air missile over Vietnam raised the stakes enormously. Now a radar that locked onto you could kill you in seconds. The American response was a dangerous new kind of mission flown by crews who called themselves the “Wild Weasels”: they deliberately flew into the teeth of the defences to bait the enemy radars into switching on, then destroyed them — the suppression of enemy air defences, or SEAD. Alongside them flew dedicated jamming aircraft, packed with electronics whose only job was to blind the missiles and the radars that guided them.

The Wild Weasel mission was as dangerous as anything in the air. The crews flew in first, ahead of the strike, and left last — deliberately making themselves targets so the enemy radars would switch on and betray their position. To kill those radars they carried a new kind of weapon, the anti-radiation missile, which homed in on the radar’s own beam and rode it down to the source. It was a deadly game of who blinked first: the radar that stayed on long enough to guide a missile might not live to fire a second one.

The spectrum as a battlefield

Today the electromagnetic spectrum is treated as a domain of war in its own right, like land, sea, air and space. Specialised jammers such as the EA-18G Growler escort strike packages; the latest fighters carry powerful electronic-warfare suites built in; and a new generation of stand-off jammers, like the one Turkey has recently unveiled, can blind an enemy from a safe distance. The fight has spread beyond radar, too: the jamming and “spoofing” of navigation signals has become routine in modern conflicts, knocking weapons and aircraft off course by feeding them false positions.

In today’s wars this invisible fight is everywhere. Whole regions are blanketed with jamming that scrambles satellite-navigation signals; drones fall out of the sky when their links are cut; precision weapons miss when their guidance is spoofed. Much of it never appears in the footage, because there is nothing to see — only the sudden failure of a machine that should have worked. The descendants of the Hamburg foil strips now fight a war made entirely of signals, waged in a part of the spectrum no human eye will ever witness.

It is no accident that electronic warfare and stealth have grown up together. Stealth makes you hard to see; jamming makes the enemy’s eyes useless. Combine the two, and you can move through defended sky almost as the Window-droppers did over Hamburg — unseen, untracked, and a step ahead of the machines built to stop you.

Sources: Royal Air Force Museum; Imperial War Museum; National Museum of the U.S. Air Force; standard histories of electronic warfare and the air war over Germany and Vietnam.