How a tube and a slide rule helped win WWII
Early on the morning of June 6, 1944, 1st Lt. Stanley Fine climbed into the B-17 designated as the lead aircraft, sat down at his radar set, and led the 401st Bombardment Group from its base at Deenethorpe, England, over solid cloud cover to Normandy.Skip to next paragraph
Subscribe Today to the Monitor
The weather over the English Channel was dreadful. Gen. Dwight Eisenhower, supreme allied commander in Europe, had agonized throughout the night about his decision to proceed with the invasion of Normandy.
Now, in murky skies above German fortifications and just ahead of Allied ground troops on the beaches, Lieutenant Fine studied the smudges on his screen and began his bombing run. From the copilot's seat, the air commander's voice crackled over the intercom, "Blind. Going in 'Mickey.' "
Sixty years later, as Americans commemorate D-Day, few know about Mickey - the nickname for the latest in a newly developed family of microwave radars that helped change the course of the war.
Small enough to be mounted in aircraft and accurate enough to "see" individual targets, microwave radar allowed the Allies to clear the sea lanes, get American troops and supplies to England, and then land those troops and weapons safely on a coastline occupied by the enemy. Without microwave radar, it's not clear that the Allies could have mounted the invasion of France in 1944.
"The thoughts of America were too much with the men going through the Normandy surf for a remarkable thing to get much notice," wrote Gen. Henry H. "Hap" Arnold, commander of the US Army Air Corps, afterward. "The final bombs that paved the way for them, dropping only a few yards ahead of the first men to hit the beaches, went down through a solid overcast of clouds, without ... so much as scratching the paint on a single rowboat in that packed armada below.... [O]ur scientists had taken from Hitler even the comfort of bad weather."
The technology - still used in some radars today - had its own heroes, including a handpicked group of British and American civilian scientists who crisscrossed the Atlantic past marauding U-boats; flew in and out of London during the Blitz to confer with fellow scientists; and flew test, training, and combat missions in military aircraft with military personnel.
As with many key inventions, the radar's beginnings were accidental. In the 1920s, scientists working on radio transmissions and communications noticed changes in their signal reception when planes flew by. Most of them recorded these observations as incidental nuisances in their notebooks, but some speculated about the cause. They soon realized that radio energy, like light, could be reflected by the surface of large objects. The audible echo - sound reflected back to its source from a large surface - works the same way.
In the decade leading up to the war, most of the advanced nations were developing radar. However, the equipment was too large and cumbersome to be mobile, and it was unable to show detail.
Scientists knew they would have to operate at higher microwave frequencies to improve the performance of their radar, but no device existed capable of transmitting sufficient power at those frequencies.
Then one afternoon in November 1939 two physicists at the University of Birmingham in England, John Randall and Henry Boot, sketched out the resonant cavity magnetron.
It took three months of shop work to build a prototype. No one knew what to expect, and at first it proved impossible to test. A blue-violet electric arc sizzled from the output lead. Then the lead melted.