Battles & Wars › Between the wars
Radar (and Britain's Chain Home)
February 26, 1935 (Daventry test); Chain Home 1937–39· Invention or discovery· Technology, codes & intelligence
Well documentedSolid records, physical evidence or scientific consensus.
Radio waves bounced off aircraft and ships reveal them far away; Britain built the first national radar warning network, Chain Home.
See it on the Battles & Wars map →What happened
Radar (radio detection and ranging) sends out radio pulses and times the echoes to find an object's distance and direction. Several countries, including Germany, the US and the USSR, developed it in the 1930s. In Britain, Robert Watson-Watt and Arnold Wilkins showed at Daventry on February 26, 1935, that a BBC transmitter's signal bounced off a Heyford bomber could be detected. By 1939 a line of tall-masted Chain Home stations along the coast could often spot aircraft over 100 km away.
Why it matters
Defenders no longer had to keep fighters patrolling; they could wait and launch on warning. Radar reshaped air and sea war, and later made air traffic control possible.
Think of it like
Like shouting in a canyon and timing the echo to judge how far away the wall is.
How we know
The Daventry test and Chain Home's build-out are recorded in Air Ministry files and Watson-Watt's memoir. A few original towers, such as at Stenigot in Lincolnshire, still stand.
Still debated
Who 'invented' radar is disputed: Germany, the US, France, the Netherlands, Japan, Britain and the USSR each developed it largely independently in the 1930s.
Inside this (5)
Connections (4)
▸Radar (and Britain's Chain Home) gave early warning in the Battle of BritainWell documented
The connection
Chain Home radar picked up German formations assembling over France, often 100 km or more away. Reports flowed to a filter room, then to Fighter Command operations rooms, where plotters moved markers on map tables and controllers ordered squadrons up. RAF fighters could wait on the ground and meet each raid, instead of wasting fuel and pilots on patrols.
When and how
Southern and eastern England, summer 1940; Hugh Dowding's Fighter Command, its Bentley Priory headquarters, and coastal radar stations.
How we know
Fighter Command records and German postwar accounts; the restored Battle of Britain Bunker at Uxbridge shows the system at work.
Debates and open questions
German intelligence underrated radar and largely stopped attacking the stations after a few raids in August 1940; why is still debated.
▸Radar (and Britain's Chain Home) spotted the incoming planes before the Attack on Pearl HarborWell documented
The connection
A US Army SCR-270 mobile radar at Opana Point, on Oahu's north shore, detected a large formation about 210 km out at 7:02 a.m. Privates Joseph Lockard and George Elliott reported it. The duty officer, Lieutenant Kermit Tyler, assumed it was a flight of B-17 bombers expected from California and told them not to worry.
When and how
Opana Point, Oahu, about 7:00–7:40 a.m., December 7, 1941; Privates Lockard and Elliott and Lieutenant Kermit Tyler.
How we know
Testimony at the Pearl Harbor investigations and the surviving radar plot record the sighting.
Debates and open questions
Whether an alert would have saved much is doubtful: it gave under an hour's warning, and Hawaii's air-defense system was not yet working.
▸Radar (and Britain's Chain Home) was answered by Electronic warfare (jamming and chaff)Well documented
The connection
Every radar sends out signals that can be detected, copied or confused. As soon as radar and radio navigation went to war, both sides built ways to jam them, spoof them or hide from them: the Battle of the Beams in 1940, 'Window' chaff in 1943, and radar-warning receivers. Each new radar has drawn a new countermeasure since.
When and how
Britain and Germany, 1940–45, then worldwide; scientists such as R. V. Jones in Britain and their German counterparts.
How we know
Wartime technical reports and postwar histories trace each countermeasure to a specific radar or beam system.
Debates and open questions
Britain held back Window for over a year, fearing Germany would copy it against British radar; whether that delay cost bomber crews is debated.
▸Stealth aircraft (F-117 Nighthawk) was designed to evade Radar (and Britain's Chain Home)Well documented
The connection
Radar works by catching reflected echoes. Stealth aircraft cut those echoes by shape: the F-117's flat, angled panels bounce radar energy away from the receiver, and later designs use smooth curves. Radar-absorbing coatings soak up much of the rest. The approach drew on a Soviet physicist, Pyotr Ufimtsev, whose 1962 equations predicted reflections from edges.
When and how
Lockheed's Skunk Works, Burbank, California, 1975–81; engineer Denys Overholser drew on Ufimtsev's published papers.
How we know
Declassified program histories and Lockheed engineers' accounts, such as Ben Rich's book Skunk Works (1994).
Debates and open questions
How well stealth holds up against low-frequency radars and networked sensors is debated; Serbia shot down an F-117 in 1999 with an old Soviet missile.