In late May, 1940, Station X warned the OIC about German Warships possibly sailing into the Atlantic. The OIC ignored it and three British ships with 1500 men were lost
In June- September 1940 although Bletchley Park was unable to become an important park of the Battle of France or Britain, they could provide important information like the number of German aircraft lost in raids. The most important message decoded in September was that the Germans had given up Operation Sealion, their attempt to invade Britain.
In 1941, Bletchley Park received reports from agents about operations in the Mediterranean. The Italians were going to invade Yugoslavia with German forces backing them up. But more spectacularly, the Royal Navy was able to take advantage of these reports and win the Battle of Matapan.
Bletchley Park also supplied information about the invasion of Crete, including the date; 20 May 1941. Unfortunately British Forces were forced to retreat, but for Station X it was a victory and showed what it was capable of.
In May 1941 the German battle ship Bismarck had attempted to attack British shipping in the North Atlantic. The Royal Navy sent forces to intercept it, but when it came in contact with HMS Hood, it was slightly damaged. Bletchley Park warned the admiralty that the Bismarck must be heading for Brest because its messages were now being sent t France. The Admiralty was not convinced until Station X cracked the code and proved that they was correct, which led to ‘Force H’ from Gibraltar to intercept and sink the Bismarck.
In 1941, the ‘Dolphin’ Naval code had been broken and the amount of British convoys sunk dropped from 282,000 tonnes of shipping to 62,000, about 15 ships.
In January 1942, Bletchley Park was unable to read messages sent by the German army in North Afrika. This resulted in British forces being forced back in North Afrika, until Station X finally cracked the German code. When German forces attempted to make a major breakthrough at Alam Halfa, the British were waiting for them. Attacks were also more successful, with 33% of shipping sunk in August and 45% in October. In December 1942 mobile Y service stations were sent to Morocco. The stations decoded German messages and warned the British about German advances and artillery. The British subsequently beat the Germans at Medenine.
Bletchley Park broke the ‘Shark’ code in December 1942 and in the first five months of 1943 more than 100 U-boats were sank and in May they were withdrawn from the Atlantic. In that month 47 U boats had been sunk by the Allies. Ultra provided the information to locate U-boats and destroy them.
In May, Station X discovered that Germans were expecting to land in Normandy, but they thought that this was just a diversion from an attack on Calais. Because of this information the Allies were able to adapt their plans.
Ultra was able to provide information about the size and location of almost all German units in Normandy, with fifty six out of fifty eight being identified. This gave the Allies an advantage at D Day (6 June).
Although many messages sent by Germans in the weeks after the landings were not read, Station X was able to give warnings of counter attacks on 10 and 12 June. However, information from Station X was ignored when 300,000 Germans were almost encircled in Normandy. This allowed the Germans to escape.
After D Day the influence of Ultra became less important. Montgomery ignored Station X information when he decided to launch Operation Market Garden, the attempt to capture the bridge at Arnhem. It was a disaster. Information was also provided about the Battle of Bulge, the counter-attack by the Germans in December 1945, though this was not the main reason for the defeat of German attack.
Ultra was a valuable source of information for the last 4 years of the war. It became more detailed and consistent and its information enabled Allied forces to survive attacks and avoid defeat. But battles were by won by Allied commanders. Bletchley Park could only provide information to plan tactics and strategy.