[L231]Led Zeppelin Early Days Latter Days

Nowadays radar is taken for granted in all nearly all aspects of aviation. And yet it is only seventy years ago that it was first being developed. Dr. Robert M. Page was a physicist working at the U.S. Naval Research Laboratory in Washington D.C. who was the original inventor of monopulse radar, preceding the work of the British by at least nine months. This was in 1934 and predates the work of Sir Watson Watt of England, though most articles and encyclopedias give Watt the credit. Early British developments in radar used existing ham technology, as they could string wire antennae by the mile along their coast facing France. They could also separate transmitter and receiver antennae as required.

In Washington, NRL scientists headed by Dr. Page improved the power and range of their earliest radar sets by using the most powerful ham radio transmitter tubes of the day and got 10-20 times the rated power out of them by designing circuits that turned them on and off for milliseconds at a time in a sequenced, 6-tube ring oscillator. Operating in the 200 MHz range, the very first test aboard the USS York spotted an airplane 45 miles away, over the horizon! This was in 1938 and by Dec. 1941, 19 such sets were aboard ships in Pearl Harbor when it was attacked. Not one was turned on. A radar trainee in a shore installation saw the echoes 15 minutes ahead of the attack and reported them, but was ignored. Higher command thought the echoes where from an inbound flight of bombers from San Francisco.

Radar was further advanced when the NRL came up with the rotating display for cathode ray tubes, called Plan Position Indicator (PPI) closely followed by the development of the "Duplexer" which allowed both transmitter and receiver to use the same antenna. To understand the importance of this, imagine standing net to a brilliant searchlight which is turned on for a fraction of a second, after which you are supposed to see reflections from the sky with you two eyes. Impossible, because you have been blinded for at least a few minutes by the brilliant flash. This was similar to the blinding of the receiver to incoming signals.

It's said that the idea for the duplexer solution to the vexing problem (blinding and destabilizing a sensitive receiver) came to Dr. Page while listening to the sermon in a Sunday morning church service. The idea so impressed him that he stopped off at his lab on his way home and recorded the idea then and there. His assistant started work on it immediately and several days later had produced a working prototype installed in a wave guide. It worked the first time. It wasn't until twenty years later that other physicists and mathematicians came up with the correct explanation for why the device worked as it did.

After the British invented the magnetron (used to this day in microwave ovens), it was combined with the duplexer, which allowed higher power and higher frequency equipment to be installed on board the early British fighter-bombers. This development was just in time to break the back of the German wolf packs in the North Atlantic that were sinking so much allied shipping.

When the U-Boats surfaced to charge their batteries, the allied planes equipped with the new more powerful radar equipment could spot them, even through cloud cover. The German subs had receivers to scan the radar frequencies and upon hearing warning signals, would dive. This actually worked against them, because there were so many signals from extended distances, that they had to ignore all but the loudest signals. The false signals were so unnerving to all aboard, that some commanders ordered their radar detectors turned off.

As their losses mounted, the sub commanders were forced to use their radar detectors. But by then, the allies had developed microwave radar, far beyond the frequency detecting capabilities of the U-Boat defensive receivers. So the subs got caught under overcasts suddenly and without warning, which led to the Black Month of May, 1943, when at least 40 U-Boats were sunk. Much of the credit for this must be given to the British and American cryptologists who broke the German Naval communication codes. The Allies knew in advance when the subs left on patrol and where they were headed, so the sub-hunters knew in advance where to look for them.

Early in W.W.II, Hitler was asked for permission to work on the development of microwave radar. When told this might take several years, Hitler refused. His policy required that scientific research produce usable applications for the military within a year's time.

Still, German intelligence and scientific personal were desperate to discover what the Allies were using. They examined downed Allied bombers for radar equipment, hoping to piece together a working set from the wrecks of Allied equipment. As Divine providence would have it, either the bomber crews or the crashes succeeded in destroying enough evidence so that it was not until very late in the war that the German technicians came into possession of more than about half a recoverable microwave radar system. By then it was too late in the war as Germany was crucially short of the required materials, not to mention the time to mass produce the sets.

The NRL also pioneered the development of fire control radar, which was responsible for winning several stunning nighttime naval battles against the Japanese in the Pacific. The early days of radar development could be said to end with the development of the Madre radar system, the last such project to use vacuum tubes. This was a low-frequency system that followed the curvature of the earth (like ham radio transmissions) and was capable of spying on Russian missile launches by returning a signal off the flaming ionized trail as the missile lifted into the sky. Later functional prototypes were able to distinguish differences of velocity among aircraft flying in formation on the other side of the North American continent; all without benefit of the modern digital computer.

The development of radar in the late thirties and through the 1940s was for the most part a co-operative effort between British and American scientists. One group or the other might seemingly lead for a short time, but then the other side would adopt the new systems and quickly go on to add their own improvements and refinements. Who should be given the most credit however is open to discussion, but what is not in doubt is the tremendous debt modern aviation owes to those early radar pioneers.