Watson-Watt and the first radar

Wars are sometimes won, before they begin, by a calculation made on the back of a train ticket. The decisive move belongs not to the general at the map but to the man at the oscilloscope, who knows what the trace ought to show and waits, in a cold field, to see whether the world will oblige him.

THE INHERITANCE OF STEAM

Robert Alexander Watson-Watt was born at Brechin in Angus on the thirteenth of April 1892, the son of a carpenter, and the great-great-great-grandson of James Watt of Greenock, whose separate condenser had set the rhythm of the industrial century. The boy grew up in a household that kept the engineer's name with the seriousness of an inheritance. He read physics at University College, Dundee, and by 1915 was at the Meteorological Office in Aldershot, tracing thunderstorms by the crackle they made in long-wave receivers. He learned, before he was thirty, that an unseen disturbance in the air will, if you arrange your apparatus carefully, announce itself on a screen. By 1933 he was scientific superintendent of the Radio Research Station at Slough, with a Scots accent he had never softened and a fondness for the unfashionable hyphen in his own name. The Air Ministry's Tizard Committee, that autumn of 1934, had been authorised to spend public money on death rays, acoustic mirrors at Dungeness, and any other contrivance that might give the island fifteen minutes' notice of a German bomber. The death rays did not exist. The acoustic mirrors heard nothing useful past four miles. The committee wrote to Slough.

THE WILKINS MEMORANDUM

On the twelfth of February 1935, Arnold Wilkins, his junior at Slough, came back from Aldershot on the afternoon train with a slide-rule in his pocket and a calculation in his head. The BBC's Empire Service shortwave transmitter at Daventry, broadcasting at fifty kilowatts on a ten-megacycle signal, ought to bounce a detectable echo off a Heyford bomber at a range of about ten miles. Wilkins put it on paper. The memorandum closed with the modest sentence Watson-Watt would read three times in the next fortnight: meanwhile a study should be made of the radio detection problem. He understood at once what the sentence concealed. Reflection had been known since Hertz; the Americans had nosed at it, the Germans had nosed at it, the Admiralty had nosed at it; nobody had yet put a transmitter, an aircraft, and a cathode-ray tube into the same morning and watched what happened. A. P. Rowe of the Tizard Committee was coming down from London on the early train on the twenty-sixth, on the understanding that if the Daventry signal bounced off a bomber the development funding would follow, and if it did not, the Ministry would return to its acoustic mirrors and its drift.

THE FIELD AT WEEDON BEC

A quarter past nine on the morning of the twenty-sixth of February 1935. A flat field at Weedon Bec, near Stowe Nine Churches in Northamptonshire, north of Daventry. Cold sun and a low ground-mist. The grass at the south edge was still rimed. An unmarked Morris van stood with its rear doors open, an antenna lashed to the roof, a cathode-ray oscilloscope fitted to the bench inside, the timing-base set to the pulse-rate of the Daventry transmitter which, by an arrangement made in London the week before, the BBC had loaned to the Air Ministry for the morning. Wilkins was in the van. Watson-Watt stood on the grass with his hands in his coat pockets and his collar turned up. Rowe stood at a little distance, not speaking, polite and unconvinced. The Handley Page Heyford, callsign Albacore, was airborne from Northolt and twenty-four minutes out at standard cruise. The plan, written by Wilkins on a half-sheet, was four runs of the aircraft south-west to north-east at six thousand feet through the beam, at intervals of fifteen minutes, beginning at half past nine.

THE TRACE

Wilkins's calculation was sound, and he knew it was sound, but soundness on paper is not the same thing as a clean sinusoid on a green screen, and the question at this hour was not whether the signal would bounce, which Maxwell had answered in 1864, but whether the oscilloscope, with its noise and its drift and its slow phosphor, could resolve the echo against the hash of the BBC's own carrier and the residual sky-noise of a winter morning in the Midlands. Rowe wanted unambiguity. Rowe would not write up an equivocal report; an equivocal report from Rowe meant no funding; no funding meant the project went back into the drawer with the death rays and the mirrors, and the Luftwaffe, which already had eighteen hundred aircraft, would keep its head-start. He watched the second-hand of his wristwatch sweep through nine forty-six and listened, against his will, for the sound of the Heyford's two Kestrels. The aeroplane came in at the predicted bearing and at the predicted moment, which was the first piece of good fortune of the morning, and as it entered the beam the cathode-ray spot on Wilkins's screen drew itself sideways into a clear modulation that ran for the duration of the aircraft's transit, about eight miles of flight at cruise, and then composed itself back into a line. Wilkins, in the van, looked at the screen and said nothing for a moment, and then said, in the British understatement, yes, that's quite definite. The Heyford made three further runs at fifteen-minute intervals. Each produced the same unambiguous trace. The four runs together took an hour and a quarter, by Watson-Watt's watch, and at the end of them the island of Britain, which had been continuous with the air above it for thirty-two years since Blériot, was an island again.

THE LINE

Rowe came up to the door of the van at the end of the fourth run with his hands still in his coat pockets. Watson-Watt, by Wilkins's later memoir, was the one who spoke. The line he gave him was: Britain has become an island again. Rowe took off his glasses, polished them on his handkerchief, and said, yes, I think it has. The two men stood at the door of the van for perhaps a minute longer; the Heyford, which had completed its work, banked away to the north for Northolt; Wilkins shut down the timing-base and the oscilloscope's trace fell to a line and held there. Rowe caught the afternoon train back to London with the report already composing itself in his head. By every careful account of the morning the line is Watson-Watt's, given in the field, in the cold sun, with the Heyford still audible to the north. It was not rehearsed. It came up out of the same mind that had read the Wilkins memorandum three times in a fortnight, and it told Rowe, in eight words, what the Tizard Committee had spent five years failing to articulate: that radio reflection, properly instrumented, restored the strategic geography that aircraft had abolished.

THE CHAIN

Rowe wrote his report that afternoon. The Air Ministry authorised the development funding within ten days. The first experimental station went on the air at Bawdsey Manor in Suffolk in August 1936; by July 1939, two months before the outbreak of war, the operational chain of fifty Chain Home stations covered the southern and eastern coasts of England from the Orkneys to the Isle of Wight. Through the summer of 1940 the chain gave Fighter Command between fifteen and twenty minutes' notice of every Luftwaffe formation crossing the Channel, and allowed the controller at Bentley Priory to scramble specific squadrons against specific raids rather than maintaining the patrols which would have exhausted the force inside a fortnight. The careful judgment of every air historian since Alfred Price is that the chain is the principal reason a numerically smaller defending force won the Battle of Britain. None of this was visible at Weedon Bec on the morning of the twenty-sixth of February 1935. What was visible was a clean sinusoid on a green screen, and a man in a coat polishing his glasses.

THE RETURN

Watson-Watt was knighted in 1942. The Air Ministry, at the end of the war, awarded him fifty-two thousand pounds for the patents. He emigrated to Canada in 1952 and lived for a time in Ontario, where in 1956, by his own delighted irony, he was stopped for speeding by a constable using a hand-held radar gun; he framed the ticket and hung it on his study wall. He came home to Inverness in 1958, kept the hyphen in his name and the Aberdeenshire vowels in his speech, and died in 1973 in his eighty-second year. He is buried at Pitlochry. The Daventry transmitter that bounced off the Heyford was pulled down in 1992. The original notebook entry of the demonstration is in the Imperial War Museum at Lambeth, the page turned to the twenty-sixth of February. At Weedon Bec, in the field north of the village, the Royal Air Force Historical Society in 1985 set a small bronze plaque into a stone at the edge of the long grass, on the line the Heyford flew. The grass grows over the stone in summer and is cut back in winter. The aphorism stands where it was spoken. The plaque, when you find it, is no bigger than a man's hand.

Decisive hours are not always loud. Some arrive in a cold field with a Morris van and a slide-rule, and announce themselves only as a clean line on a green screen, witnessed by three men, one of whom understands at once that the geography of his country has just been restored.