Watson · 1935
Watson-Watt and the first radar
On the morning of the twenty-sixth of February 1935, on a flat field at Weedon Bec, near the village of Stowe Nine Churches in Northamptonshire, an Air Ministry team under Robert Alexander Watson-Watt, scientific superintendent of the radio department of the National Physical Laboratory, demonstrated to a single Air Ministry observer (A. P. Rowe of the Tizard Committee) that a Heyford bomber flying through a beam of BBC Empire Service shortwave at twenty-five miles range produced a detectable echo on a cathode-ray oscilloscope inside an unmarked van. The flight, of two minutes, the echo, of eight miles' duration on the screen, and the corresponding deflection of the cathode-ray spot were the first practical British demonstration of what would within the year be called Radio Direction Finding and would, by the end of the decade, be called radar. The Air Ministry awarded Watson-Watt and his Slough team the immediate development funding for the system that became Chain Home, the chain of fifty British radar stations that detected and tracked the Luftwaffe formations entering British airspace through the summer of 1940. Watson-Watt was Aberdeenshire-born, the descendant of James Watt the engineer, in his forty-third year on the morning of the demonstration. Tradition holds that A. P. Rowe, on returning to London that afternoon, said to the Air Member for Research at the Air Ministry: *Britain has become an island again.*
It is a quarter past nine on the morning of the twenty-sixth of February 1935, in the long grass at the south edge of an Air Ministry test field at Weedon Bec, north of Daventry in Northamptonshire, in mist and a cold sun. He is forty-two years old. He is Robert Alexander Watson-Watt, born at Brechin in Angus on the thirteenth of April 1892, son of a carpenter and the great-great-great-grandson of James Watt of Greenock, scientific superintendent of the Radio Research Station at Slough, in the eleventh week of the project the Air Ministry's Tizard Committee has set him on quietly since the autumn of 1934, namely whether the new science of radio reflection can be turned into an early-warning system for incoming aircraft.
The memorandum from his junior at Slough, Arnold Wilkins, dated the twelfth of February, has, on a calculation Wilkins did with a slide-rule on the train back from a visit to Aldershot, established that the BBC's existing 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. The memo, which Watson-Watt has read three times in the past fortnight, ends with the modest sentence: meanwhile a study should be made of the radio detection problem. The Tizard Committee in London, which can authorise development funding only if there is a demonstration, has sent A. P. Rowe down from London on the early train this morning to see whether the Daventry signal can in fact bounce off a bomber.
On the field is an unmarked Morris van fitted out by Wilkins with a cathode-ray oscilloscope, a receiving antenna mounted on the roof, and a fixed timing-base set to the pulse-rate of the BBC's Daventry transmissions. The transmitter has been borrowed by the Air Ministry from the BBC for the morning. A Handley Page Heyford heavy bomber, callsign Albacore, is to fly a steady course south-west to north-east at six thousand feet through the radio beam, four times, at intervals of fifteen minutes, beginning at half past nine. Wilkins is in the van.
He thinks: Wilkins's calculation is sound. The signal will bounce. The question is whether the oscilloscope can resolve the echo against the noise.
He thinks: Rowe is a sceptic. Rowe wants the signal to be unambiguous. If the trace on the oscilloscope is ambiguous, Rowe will not write up a positive report and the development funding does not come.
He thinks: if the development funding does not come we have wasted six months and the Air Ministry goes back to the drift of the past five years on early warning, which is the committee's interest in acoustic mirrors at Dungeness.
He thinks: the Heyford is in the air at Northolt now. The Heyford is twenty-four minutes from Weedon at standard cruise.
The first run of the Heyford comes through the beam at nine forty-six. The cathode-ray trace, by Watson-Watt's witness in the van, shows a clear sinusoidal modulation that runs from the moment the aircraft enters the beam to the moment it leaves, a duration of about eight miles of flight at the aircraft's cruise. The trace is unambiguous. The aircraft has come in at the predicted bearing and at the predicted moment. Wilkins, in the van, says nothing for a moment, then says, in the British understatement: yes, that's quite definite.
The Heyford makes three further runs through the beam at fifteen-minute intervals, each producing the same unambiguous echo. Rowe, who has been standing on the grass beside the van with his hands in his coat pockets, comes up to the door at the end of the third run. Watson-Watt, by Wilkins's later memoir, is the one who speaks, and the line he says is: Britain has become an island again. Rowe, by Wilkins, takes off his glasses, polishes them on his handkerchief, and says: yes, I think it has.
Rowe wrote the report for the Tizard Committee that afternoon. The development funding was authorised within ten days. The first experimental Chain Home radar station was on the air at Bawdsey Manor in Suffolk by August 1936; the operational chain of fifty Chain Home stations covered the southern and eastern coasts of England by July 1939, two months before the outbreak of war. Through the summer of 1940 the Chain Home stations gave the RAF Fighter Command between fifteen and twenty minutes' notice of every Luftwaffe formation crossing the Channel, allowed the controller at Bentley Priory to scramble specific squadrons against specific incoming raids, and is, by the careful judgment of every air-historian since Alfred Price, the principal reason that the Battle of Britain was won by a numerically smaller defending force.
Watson-Watt was knighted in 1942. The Air Ministry awarded him fifty-two thousand pounds at the end of the war for the patents on the system; the original notebook entry of the demonstration of the twenty-sixth of February 1935 is in the Imperial War Museum at Lambeth. He emigrated to Canada in 1952 and lived out his life in Ontario; in 1956, by his own irony, he was given a speeding-ticket by an Ontario police constable using a hand-held radar gun. He framed the ticket and put it on his study wall in Inverness, where he had retired by 1958. He died in 1973, eighty-one years old, and is buried at Pitlochry. The Daventry transmitter that bounced off the Heyford in 1935 was demolished in 1992. A small bronze plaque at the field at Weedon Bec, put up by the Royal Air Force Historical Society in 1985, marks the site of the demonstration. The line Britain has become an island again is, by every careful witness of the morning, his.