Codebreaking and Secret Weapons in World War II

By Bill Momsen

© 1993 - 2001 Copyright Nautical Brass. All rights reserved.

Chapter III: 1941

Early in 1941, England's position was truly desperate. Civilian rations had been cut, cut again, and cut once more. The dreaded invasion had been postponed, but was still a possibility. English cities were being bombed nightly. The Germans commanded a great arc stretching from Norway to the Spanish border, from which they could deploy their U-boats and Luftwaffe. The RAF, thanks to the brilliant direction of Sir Hugh Dowding (aided by his supply of Ultra and radar information), was still operative. If the Battle of Britain had not been won, the invasion might have taken place, and England could have been forced to capitulate. There was a further trial ahead, the Battle of the Atlantic. Once again, if England's life line had been cut, surrender might have been inevitable.

RDF (Radar)

In the 1930s the only way to detect hostile aircraft approaching the English coastline was by sound location or visual sighting, both of which were inaccurate and of no use at all if cloud cover was present. By the spring of 1939, however, a chain of aircraft detection stations had been set up along the coast. The cover name for the operation was "RDF" (Radio Direction Finding). In operation, a train of radio pulses was transmitted, bounced off the target, and detected by a receiver. The time between transmitted and received pulses was used to calculate the distance from the ground station, which could warn of incoming enemy planes 100 miles away at night or in periods of fog or storm. "RDF" was soon replaced by the American acronym RADAR (RAdio Detection and RAnging), and the term RDF applied to passive directional receivers which could take bearings on ships and ground stations.

The very short intervals to be measured were displayed on a CRT (Cathode Ray Tube, the forerunner of the TV picture tube). A beam of electrons was rapidly swung back and forth, impinging on a phosphor screen which glowed when electrons struck the phosphor. The returning pulses moved the electron beam up, painting a "blip" on the screen. The time between blips represented distance to the target; in fact the display screen was calibrated in miles. Various improvements were made so range, height and bearing could be measured.

German Radar

The Germans had set up their own radar stations, but employed them in anti-shipping operations. German radar operated on a much shorter wavelength (1 1/2 meters to 50 cm) than the British (an unbelievable 10 meters!) and was transmitted from bowl-shaped parabolic antennas. To determine if the British had radar, the Graf Zeppelin (a large dirigible) made several flights up the coastline, listening for signals. The British were tracking the largest blip they had ever seen on their radar scopes. The Germans found nothing and concluded there was no British radar, which would cost them dearly once they started their attacks. They had been searching for the wrong wavelength!

They had observed British coastal installations sporting some rather odd-looking antennas, none of which were bowl-shaped, and decided they couldn't possibly be connected with radar. Besides, they were difficult to attack. This was to be their downfall in the Battle of Britain.

Knowing German plans from Enigma intercepts and radar information, the British were able to keep their fighters on the ground until the bombers showed up. German pilots couldn't understand how the British seemed to know exactly where they were going to be and when.

ASW

At the start of the War there was not much that could be done about the U-Boat menace, and it soon became obvious that Anti-Submarine Warfare (ASW) must be a high priority. By the end of 1940 the British had developed 1 1/2 meter radar sets fitted to their night fighters. They could pick up a surfaced submarine five miles away. U-Boats were sunk in significant numbers as they traversed the Bay of Biscay on the surface. Because of "clutter," radar pulses reflected by the sea, at ranges less than a mile, contact was lost. During the day this was of no consequence, as the target could be sighted visually. The U-Boats soon learned to travel submerged during the day, and kills were reduced accordingly.

Wing Commander Leigh of the Coastal Command proposed placing a powerful movable searchlight in the nose of the plane to illuminate the submarine at night. After the usual considerable battles with officialdom, the Leigh light was adopted. The surfaced sub was acquired on radar, and when contact was lost at about a mile the light was switched on. The effect on a submarine crew was considerable - cruising along with no warning, a blinding 22 million candlepower light, and depth charges.

As with any new weapon, it is only effective until a countermeasure is developed. The Germans soon equipped their subs with "Metox" receivers, which picked up the radar pulses, and gave plenty of warning to dive to safety.

The Supply Line

Prior to the outbreak of hostilities, England had established a balance of trade with the western hemisphere. Manufactured goods were traded for raw materials such as oil, iron and grain. With the outbreak of war, this balance shifted. Imports increased while exports decreased as manufacture moved to the production of weapons. This excess of imports over exports was paid for by transferring England's gold reserves to the west. But those reserves, not unlimited, were rapidly becoming exhausted. German submarines were taking a fearful toll of merchant shipping.

Prime Minister Winston Churchill realized that England's only salvation was to involve the United States in the conflict. Franklin D. Roosevelt, President of the United States, was sympathetic to the British cause, but his hands were tied by the complexities of American politics. It was a delicate situation - how could America supply vital war materiel to Great Britain and, at the same time, maintain its neutrality?

Across the Atlantic

Roosevelt knew that America's involvement in the global conflict was inevitable, but the country was in no mood for another war. Furthermore, there was no guarantee that England would not be defeated. Roosevelt not only had to face an isolationist Congress, but worried that he would not be elected to a third term, realizing that switching national leaders on the eve of war would be most unwise.

The Irish Free State (Republic of Ireland, or Eire) had been established in 1921, leaving Northern Ireland still closely tied to Great Britain. As part of the settlement, some naval bases in the Irish Republic were occupied by the British. At the start of World War II, the Irish Republic flatly refused to become involved unless the whole island was united under their rule. The British declined, and relinquished their bases. However, they still maintained facilities in Northern Ireland, which guarded the vital Atlantic approaches. (The Republic of Ireland managed to stay neutral throughout World War II.)

Anti-war Sentiments

In view of this, it was not surprising that Irish-Americans resisted the United States siding with the British. Irishman Joseph Kennedy, American Ambassador to Great Britain, was convinced that England could not hold out much longer. Some industrialists were looking forward to lucrative sales to a Nazi dominated Europe. Other Americans holding anti-British sentiments were German-Americans and American Communists (in view of Germany's non-aggression pact with Russia). Irishman John L. Lewis of the powerful United Mine Workers Union, controlled 5 million anti-Roosevelt votes. Besides, if England's fall was a foregone conclusion, why send military aid that would only fall into German hands?

Roosevelt wanted the freedom to selectively supply arms to other countries, but Congress insisted on a mandatory embargo to all countries.

Aid to Britain

Finally the U.S. arms embargo was modified to allow a "cash and carry" policy, declaring certain arms "surplus," which Britain could purchase for cash. There were other ways to get around the arms embargo; in September, 1940, fifty American four-stacker destroyers were traded for the U.S. use of British bases.

As British supplies of U.S. dollars and gold reserves were rapidly depleted, technology was traded for credit. The magnetron, an essential radar component, had been invented by the British, but was traded to the U.S. for arms.

Nov. 5, 1940, Roosevelt was elected to a third term, the first ever for a U.S. President, his hands now free to send vitally needed aid to Great Britain. On Jan. 10, 1941, the "Lend Lease" program was instituted. By War's end 30 billion dollars had been lent to Great Britain.

Cryptanalysis in the U. S.

Prior to World War I the United States had been regularly monitoring and decoding messages between foreign diplomats in the U.S. and their home countries.

In World War I, the Japanese were aligned with the Allies. At an arms limitation conference between the major powers at the conclusion of World War I, they wanted parity with Great Britain and the United States. However, decoded messages showed they would settle for a ratio of 1:1:6. Knowing their bottom line, the other powers insisted on this reduction, which was to have great repercussions for Japanese naval strength at the start of World War II.

In 1928 a commercial Enigma was, through great foresight, purchased and shipped to America before it was withdrawn from the market. On May 1929 Henry Stimson, the new Secretary of State, naively stated "gentlemen do not read each other's mail" and closed "The Black Chamber" (a generic term for cryptanalysis operations), which was headed by Herbert Yardley. With his command disbanded, a disaffected Yardley wrote The American Black Chamber in 1931. The book is an exposition, in detail, of the cryptanalytical techniques used to break foreign codes. Ostensibly, Yardley wrote the exposé because there was no reason to keep the techniques secret. The book caused quite a sensation in its day!

Fortunately, its functions were transferred to the Signal Intelligence Service under the brilliant direction of William Friedman, and codebreaking efforts continued as if nothing had happened. Born Wolfe Friedman in Russia, his first name was changed to William when his family emigrated to the United States in 1892. He was appointed Chief Cyptanalyst of the Signal Corps in 1922. Predictably, Friedman's efforts were primarily concerned with Japanese traffic. Although Friedman is generally credited for breaking the Japanese codes, his subordinate, Frank Rowlett, was mainly responsible for the effort.

Oddly enough, the Germans had actually demonstrated their Enigma to Major P. W. Evans of the U. S. Army Signal Corps in October, 1930. They also showed him a large 10-rotor machine and an even larger 20-rotor device, neither of which was ever used during WWII. Why would they have done this? Was it arrogance on their part, "knowing" that Enigma codes were unbreakable?

Japanese Codes

Note: The following section is excerpted from "Pearl Harbor, Mother of All Conspiracies", by Mark Willey.