The situation in Europe in May 1941, where our story begins, was extremely grave. Here is a brief history of the events that preceded it. 

In 1933 The Nazi Party under Adolf Hitler came to power in Germany.  Hitler began to rebuild the military in direct violation of the Treaty of Versailles. The Treaty of Versailles was a peace treaty signed by Germany and the Allied powers in 1919 after the end of World War I. The treaty required German disarmament and allowed for the occupation of the Saarland, a province of Germany, by France. The French occupation was subject to a plebiscite to be held in 1935.  

In 1935 the Saarland voted overwhelmingly to rejoin Germany. In 1935 Hitler also repudiated the treaty and sped up militarization.

In March 1938 Germany annexed Austria.

In September 1938 Germany annexed a part of Czechoslovakia known as the Sudetenland.

In March 1939 Germany seized the remainder of Czechoslovakia. The western democracies finally began to realize the full intent of Hitler’s ideals.

In the same period, Italy, an ally of Germany, occupied Albania. 

After a blitzkrieg assault Germany occupied Poland in September 1939. France, Britain and other countries of the commonwealth declared war on Germany. 

The time between late April 1939 and April 1940 was known as the ‘Phony War’. The war had been declared, but neither side launched any significant attacks. Germany built up forces to invade France while France established defenses behind her Maginot Line (a series of strong fortifications on the French-German Border).  Since the Maginot Line did not extend beyond that border, the French positioned their more mobile forces, including the British Expeditionary Force, on the Belgium Border. 

German forces attacked and occupied Denmark in April 1940 and Norway in June 1940.

May 1940 saw another blitzkrieg attack, this time on Belgium, the Netherlands and France.

German Army Group A (containing the majority of the Panzer Units) attacks through the Ardennes Forrest and cut off two French Armies and the British Expeditionary Force from the rest of the French Forces. These troops either surrendered or were evacuated at Dunkirk.

A numerically superior French army was routed and France fell in June 1940. 

Japan, Germany and Italy signed a mutual defence treaty in September 1940 and became known as the Axis powers. The Soviet Union expressed an interest in joining and even made an explicit proposal. The Axis did formally expand in 1940 to include Hungary, Slovakia and Romania, but not the Soviet Union. 

America had not yet entered the war. Britain stood alone, preparing for a German invasion. 

Britain was pounded by German air raids. The Battle of Britain was fought from July to October 1940. It was an attempt by Germany to gain air superiority, by knocking out British air fields and fighter planes. The Battle of Britain was followed by the blitz, a sustained bombing of British targets that continued until May 1941.


The Blitz began with the bombing of London for 57 consecutive nights. By the end of the bombing campaign, over a million houses in London were damaged or destroyed, and over 43,000 people were killed in British towns. Here are some photos depicting the Blitz on Britain.


In the North Atlantic, U-boats patrolled the seas cutting off essential supplies to Great Britain.


U-boats spent most of their time on the surface but could dive under water to avoid detection or attack. 

In fact, this Battle of the North Atlantic  had a profound outcome on the war. The situation was clear: Britain needed supplies coming from the Americas, Germany wanted to prevent those supplies from arriving. 

The Allies sent merchant ships across the North Atlantic to supply Britain, and later in the war, to supply the military campaigns in North Africa and Italy, and also to supply the Soviet Union after she had been attacked by Germany and joined the Allies. The Germans countered with U-boats that sank Allied supplies.
 
Without enough food, fuel, raw material and arms supplies, Britain would be ill equipped to withstand a German invasion. With too many boats sunk, the Allies could not supply both the civilians with food and basic supplies, and the armed forces with war material. 
 

With too many boats sunk, plans for later in the war would be in jeopardy. 

There would be no North African campaign without sufficient supplies sent by ship. The Soviet Union, which carried the land war between late 1941 and the Allied invasions at Normandy in June 1944, needed resupply by ship through Murmansk. 

By 1943 the situation was so dire that at the Casablanca Conference of Allied leaders in January, 1943, the defeat of the German U-Boats was made the highest priority of the war effort. 

Winston Churchill wrote of the Battle of the North Atlantic that “the only thing that ever really frightened me during the war was the U-boat peril”.

Initially, the U-boats were extraordinarily successful. And this despite inadequate preparation and only a small number of operational vessels. 


In the seven months from June to December 1940, U-boats, supplemented by mines (which the U-boats sometimes laid), aircraft and surface vessels sunk over three million tonnes of Allied shipping. 


In this grim context, a program directed by Alastair Denniston at Bletchley Park began working on the decryption of German secret codes. He assembled a team that was very different from what would normally be considered a war time unit. They included mathematicians, puzzle solvers and chess players: people who could think hard and think different. 

The most well known of the group was Alan Turing. 

Bill Tutte joined this team in May 1941. 

Bletchley Park also contained large numbers of women who performed computational tasks associated with decryption, early “computers” as it were.  And there were logistical staff who did everything from manage teletype machines to clean.
 
Alan Turing spent most of his time attacking a code used by the German Navy, Enigma. The Enigma machine was a rotor cipher. 

A great deal of traffic encrypted by Enigma could be read decrypted and read by British analysts. This information was relayed to the British Admiralty who could tell convoys to re-route to avoid locations where submarines were known to be present. It also allowed Allied ships and aircraft to attack the U-boats and force them to submerge.

Running on the surface U-Boats could outrun most merchant ships but submerged they were simply too slow. To save a convoy, it was enough to force U-boats underwater out of attack range.

When my father crossed to Europe in 1940, it is quite possible that the cryptographers at Bletchley Park provided unknown but essential assistance to the ship. 
 
 
My uncle’s ship almost certainly made use of decrypted Enigma traffic in its protection of convoys and in its sinking of two U-boats: U-90 in July 1942 and U-87 in March 1943.

However, even accurate intelligence is not always enough. On 16 September 1942, the HMCS St. Croix went to the aid of convoy ONS 18 and later ON 202, both under heavy, coordinated attacks by U-boats. U-boats that attacked in such a manner were called wolf packs. The battle between the convoy escorts and the wolf pack lasted six days with losses to both sides. 

HMCS St. Croix was the first escort to be sunk, struck three times by torpedoes on 20 September. HMS Itchen went in to pick up survivors and was protected during the rescue operation by HMS Polyanthus. Polyanthus was sunk by U-boats during the rescue operation. Itchen was forced to retreat and returned on September 21 to pick up survivors. The following day, Itchen was torpedoed. Of the 147 personnel on board the St. Croix, exactly one survived the battle. 
 

William Tutte worked on a different family of secret codes that the British cryptographers named “Fish”. Unlike the Enigma machine whose physical structure was known, the Allies had no such information about Fish. Over time, it became clear that Fish was being used differently than Enigma was used. It carried longer, higher-level communications. William Tutte, using only samples of the messages, was able to determine the structure of the encryption device. Tony Sale writing in the 10 May 1997 edition New Scientist, described this as the “greatest intellectual feat of the war”. 





