From the Desk of Norman Fine: The Most Influential Invention of World War II

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Norman Fine is a retired electronics engineer, founder of a high-tech company, and the editor and publisher of an annual engineering design guide series in the 1990s. He is the author of the forthcoming book Blind Bombing: How Microwave Radar Brought the Allies to D-Day and Victory in World War II (Potomac Books, December 2019). 

Most readers of World War II histories are by now familiar with the many breakthrough and turning point stories that emerged after those six years of conflict, 1939−1945. Widely known are the scientific accomplishments of the Polish and British code breakers that decrypted Germany’s Enigma Code and the creative though sometimes outlandish plots by British and American spy agencies, all of which played important roles in the ultimate Allied victory. But if a historian had to name the single invention made at the outset of the war that proved most influential in getting the Allies to D-Day and finally winning the war, it would have to be the resonant cavity magnetron. Without it, the world would not be marking the seventy-fifth anniversary of D-Day on June 6, 2019. Yet how many readers have ever heard of it?

I learned of the resonant cavity magnetron by reading some rather technical books. We need not delve into the science of it to appreciate what it accomplished; but allow me to go back a few years and recreate the trail that led me to write this story.

Shortly after the end of World War II, my uncle David took my cousin and me to an open house at his alma mater, the Massachusetts Institute of Technology (MIT), in Cambridge. MIT had invited the community to see many of the new technologies that had been developed there during the war years. At the open house, special efforts had been made to capture the interest and imagination of youngsters. I can vouch for their success with at least one youngster, for it was on that day I knew I would become an engineer.

Years later, after graduating from Dartmouth’s Thayer School of Engineering, a colleague and I as consultants to Raytheon found ourselves on a team tasked with designing an improved large-screen radar display scope for use by air traffic controllers in the FAA’s next generation system. The team was to redesign all the old vacuum tube circuits and replace them with new transistorized circuitry. The advent of the transistor had rendered the large, power-hungry vacuum tube obsolete. By the time the project was over, we had designed the first fully transistorized radar information display. With the brashness of youth, my associate and I decided to start our own company.

It was the period of the Cold War, and aerial reconnaissance was a high-priority mission for the military. Therefore, much of our work in the early years was under contract to the U.S. Naval Research Laboratory, the U.S. Air Force, and prime contractors to these agencies for precision, film-recording radar and infrared scopes. Working at a state-of-the-art level, however, we had one problem―a scarcity of published design guides and reference texts. Searching the literature, the best we found was one volume from a set of books known as the Radiation Lab series, which MIT had published right after World War II. Even though it was written in the era of vacuum tube circuit design, it was all we had and it was helpful in our work.

My search through radar literature was also luring me in directions apart from my original purpose. I found Radar in World War II by Henry Guerlac, a two-volume history of the MIT Radiation Lab (Rad Lab) and its development programs. I discovered that the Rad Lab had been organized at MIT in 1940 for the sole purpose of designing advanced radars for the war effort―so-called microwave radar. The volumes described the scientists’ accomplishments and how they produced results in an astonishingly short period of time and under great pressure.

I learned that a gadget called the resonant cavity magnetron—invented in England and secretly revealed to high-ranking American scientists and military officers just months before the United States entered the war—was the revolutionary device around which microwave radar sets were designed at the Rad Lab. Both Germany and Japan had radar as well, but it was primitive by comparison. For the enemy, it was analogous to going to war with muskets against forces equipped with high-powered rifles. And not a clue as to what a rifle even was.

Germany swept over Europe, and Britain’s survival was seriously in doubt by statesmen and military leaders on both sides. Fighting alone for the first year, Britain made a heroic stand. President Roosevelt, hobbled by a powerful mood of isolationism in the United States, helped Britain immeasurably by sending needed military supplies across the Atlantic. Germany answered with the U-boat, and the shipping lanes became a sea of carnage.

The microwave radar systems of both British and American designs that were emerging from the laboratories were met first with indifference and even resistance by some Allied military leaders. But the revolutionary new radars were to prove themselves by conquering the two major obstacles to D-Day without the enemy even understanding how. First, during the Battle of the Atlantic, they located U-boats in the immensity of the oceans and destroyed them, thereby  reopening the shipping lanes to Britain. Nazi leaders were bewildered by their U-boat losses.

The second major obstacle to D-Day was the typically overcast European weather, which, from 1941 through 1943, caused the scrubbing of 70-to-80 percent of all planned bombing missions. As 1943 rolled over to 1944, the Nazi war-making infrastructure remained intact, and the Luftwaffe continued to be a potent force. Both had to be destroyed before landing Allied troops on the Normandy beaches.

The first microwave radar­–equipped b-17s trickled into the U.S. Eighth Air Force Heavy Bomber Command in England. Twelve prototypes assembled and somewhat crudely installed into the planes by Rad Lab technicians arrived in December, followed by the first production model at the end of January. More radar-equipped bombers―”Mickey” ships―arrived over the next six months. Their arrival completely changed the bombing protocols of the Eighth Air Force.

From the beginning of 1944 until the end of the war in Europe, overcast weather would no longer ground the heavy bomber. A Mickey-equipped Pathfinder plane led every bomber formation on every mission, no matter the weather. The Pathfinders navigated by radar to their targets through the thick European weather, “saw” the targets on their radar scopes through the cloud cover, and dropped the first bombs and marker flares through the overcast. The bomber crews in the formations blindly following the Pathfinders dropped their own bombs on the Pathfinder’s flares as an act of faith.

In truth, there had been precious little faith in radar-guided bombing at the start due to the usual startup problems and confusions. But the bombers flew, attacking airfields, manufacturing plants, oil refineries, and railroad marshaling yards. The Luftwaffe was forced into the air to oppose the bombers and were shot down. Just six months after the introduction of radar bombing there were scarcely any German planes in the sky or any fuel to run them and few experienced pilots to fly them. On June 6, 1944, the Allies launched the largest land invasion of combat forces by sea in all of history. It was D-Day, and by nightfall the Allies finally had a foothold on the enemy-occupied continent.

Knowing that my uncle Stanley had been a highly decorated b-17 navigator, I called him and asked if he had ever come across one of the Mickey-equipped b-17 crews or if he had known any of the Mickey navigators. I wanted to talk to one if at all possible.

After a moment of silence he said, “Norman, I flew the first production model of the Mickey radar to England to begin my combat tour. I was a Mickey operator.”

The trail that had begun in simple curiosity had brought me to my own uncle. With this new offensive weapon in his hands, and with his lead b-17 prominently in full view of defending German fighter planes, he had led wave after wave of heavy bombers through flak-filled skies to their targets.

I had a little-known story that begged to be written for a non-technical readership; I had access to one of the warriors who pioneered the use of radar as an offensive weapon; and I subsequently located the former Rad Lab scientist who designed the Mickey radar living in the town right next to me. I had what I needed to tell a remarkable story.

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