Allies and German Axis powers fought brutally with the Suez-Canal at stake. 1942: General Montgomery’s forces drove General Rommel's German forces from Egypt.

"It became obvious from Ultra that Rommel intended his final drive to Alexandria in the
full moon of August by a sweep through the Southern flank The Army Commander
accepted the evidence and made his arrangements. Believing that the confidence of
his men was the prerequisite of victory, he told them with remarkable assurance how
he enemy was going to be defeated." - Officer Brigadier Williams

Alan Turing, Enigma, and the Breaking of German Machine Ciphers in World War II. 31 Dec. 1997

Lieutenant General Bernard Montgomery, GOC V Corps, with war correspondents during a
large-scale exercise in Southern Command, March 1941. Imperial War Museum, Mar. 1941

U.S. Air Force. P-40s at their airbase in Egypt. NATIONAL MUSEUM
OF THE UNITED STATES AIR FORCE, Oct. 1942

Erwin Rommel and Hitler. getty images, 17 Mar. 1943

"expressed the opinion that, had we not had the 'U' [Ultra] service, Rommel would certainly have got through to Cairo." - Commander Auchinleck

Alan Turing, Enigma, and the Breaking of German Machine Ciphers in World War II.

"Enigma" ["Enigma"]. Enigma.umww.pl, Ministry of
Foreign Affairs of the Republic of Poland, 2017

“We then heard on the radio
that we landed on North Africa,
and we said 'ah that's what we were doing.'”
- Batey (Film 4)

Batey, Mavis. "Mavis Batey - Film 3, 4, 10 ,12." Legasee.org.uk, Netfrux Technologies

1940: Germany declared "unrestricted submarine warfare" on Allies. For six years, the “Battle of the Atlantic” raged, being

"among the grimmest, most merciless, and most blood-thirsty of the entire war."

Budiansky, Stephen. Battle of Wits : The Complete Story of Codebreaking in World War II. New York, Touchstone Book, 2002.

Winston Churchill Archives Trust. Extract from the British government's weekly
summary of the military situation in August 1940. Aug. 1940. Churchill Archives

1942: German U-boats sank a half-million tons of shipping, and Allies’ much-needed supplies never reached their shores.

Budiansky summarizes sailors’ attitudes:

"if you were on a ship carrying iron ore, you slept on deck because it would sink like a rock
when hit, and there would be only seconds to scramble overboard. If you were carrying
an ordinary cargo, you could sleep below, but you left your clothes on and the door open.
f you were aboard a tanker, you got undressed, shut the door, and got a good night's sleep
because if you were hit, you would be blown to bits anyway."

Budiansky, Stephen. Battle of wits : The Complete Story of Codebreaking in World War II. New York, Touchstone Book, 2002.

"A solution was badly needed. Germany was building more and more U-boats, and they
were sinking more and more ships. Bletchley's hope was further kept up by the bit
and pieces of German cryptography that dribbled in from time to time."

Kahn, David. Seizing the Enigma : The Race to Break the German U-Boat Codes, 1939-1943. Boston, Houghton Mifflin, 1991.

U-BOATS: Breaking the Enigma Code Allowed Brit Ships to Evade German
U-boats. Alan Turing Father of Modern Computer Science, vixra.org

February 1942: Germans complicated naval Enigma - incorporating space for a fourth rotor, resulting in a code blackout for Bletchley. They could no longer read naval ciphers. It didn't render bombes useless; they simply ran too slow to analyze what would be all four-rotor possibilities.

"In 1941, Hut 8 had given sight to the blind, and if this experience had been
traumatic, the taking of sight away was an even more cruel blow."

Hodges, Andrew. Alan Turing - the Enigma. Princeton, New Jersey, Oxford : Princeton UP, 2014.

"Who Were the Real Enigma Heroes?" Thehistorypress.co.uk, History Press

Although this blackout lasted a year, it lifted with U-559’s sinking, resulting in Enigma codebook captures. October 1942: Two men - Fasson (left) and Grazier (right) - retrieved these codebooks from sinking German U-559, losing their lives to obtain this enemy information. These “pinchings” revealed the fourth rotor remained stationary during messages; Bletchley broke their blackout. November 24th: messages were decoded quicker than a day instead of several because the Germans hadn't utilized four-rotor full potential.

"Who Were the Real Enigma Heroes?" Thehistorypress.co.uk, History Press

"The cryptanalysts learned that the four-letter indicators for regular U-boat messages were the same as the three-letter indicators for weather messages that same day except for an extra letter. Thus, once a daily key was found for a weather message, the fourth rotor had to be tested only in twenty-six positions to find the full four-letter key."

Kahn, David. Seizing the Enigma : The Race to Break the German U-Boat Codes, 1939-1943. Boston, Houghton Mifflin, 1991.

Bletchley discovered U-boat positions and could reroute convoys. While this didn't end the Battle of the Atlantic, it certainly aided Allied causes. For example, shipping losses dramatically declined.

Hodges, Andrew. "Alan Turing: The Enigma." Turing.org.uk

"... the single most important cryptologic
breakthrough of the entire war."

Budiansky, Stephen. Battle of Wits : The Complete Story of
Codebreaking in World War II. New York, Touchstone Book, 2002

"Enigma-derived intelligence enabled the American and British navies to break the death grip that the German navy held on Allied military and merchant shipping in the Atlantic." - Prof. Garlinski

Bateman, Gary M. "THE ENIGMA CIPHER Machine." American Intelligence Journal, vol. 5, no. 2, 1983, pp. 6–11. JSTOR

"A new development is that the naval section expect to be able to read the submarine traffic again shortly through the weather messages." - Head of Met Section

Budiansky, Stephen. Battle of wits : The Complete Story of Codebreaking in World War II. New York, Touchstone Book, 2002.

"Like poker, the U-boat war was a game of imperfect information, with bluffing and guessing. It was also a game in which, by August 1941, the British had placed a mirror behind the opponent's hand, and was able to cheat by looking at almost all the German cards."

Hodges, Andrew. Alan Turing - the Enigma. Princeton, New Jersey, Oxford : Princeton UP, 2014.

Keystone Getty Images. Sea Convoy. 15 Nov.
1941. Churchill Archives

"The intelligence which has emanated from you before and during this campaign has been of priceless value to me...It has simplified my task as a commander enormously… It has saved thousands of British and American lives, and, in no small way, contributed to the speed with which the enemy was routed and eventually forced to surrender."- Eisenhower

Kirka, Danica. "British Codebreakers show Eisenhower letter on their success." Military Times, 15 Mar. 2016,

Historians estimate Bletchley’s code-breaking operations, especially the breaking of naval Enigma, shortened war-time by two years.

1944, Allied forces invaded Normandy in the largest seaborne invasion. Beforehand, Allies facilitated a deception operation, compelling Hitler to believe their target was Calais.

Brigadier Williams stated Ultra

"was the only source revealing the enemy's reactions to a cover plan. Without Ultra we should never have known.”

Alan Turing, Enigma, and the Breaking of German Machine Ciphers in World War II. 31 Dec. 1997

"Bletchley Park reveals Decrypted Nazi D-Day messages." Bbc.com, BBC News
Services, 6 June 2019

During the Normandy Landings, Bletchley furiously decoded Enigma messages, passing them to commanders. Without ULTRA’s power, D-Day may have failed.

“The intelligence which has emanated from you before and during the campaign has been of priceless value to me. It has simplified my task as a commander enormously. It has saved thousands of British and American lives…’ - General Eisenhower

Powell, Lewis F., and Diane T. Putney. ULTRA and the Army Air Forces in World War II : An Interview
with Associate Justice of the U.S. Supreme Court Lewis F. Powell, Jr. Honolulu, UP of the Pacific, 2005.

Back

"expressed the opinion that, had we not had the 'U' [Ultra] service, Rommel would certainly have got through to Cairo." - Commander Auchinleck

​​​​​​​​​​​​​​“We then heard on the radiothat we landed on North Africa,and we said 'ah that's what we were doing.'”​​​​​​​- Batey (Film 4)

"among the grimmest, most merciless, and most blood-thirsty of the entire war." ​​​​​​​

"A solution was badly needed. Germany was building more and more U-boats, and they​​​​​​​were sinking more and more ships. Bletchley's hope was further kept up by the bitand pieces of German cryptography that dribbled in from time to time."

"In 1941, Hut 8 had given sight to the blind, and if this experience had been​​​​​​​traumatic, the taking of sight away was an even more cruel blow."

​​​​​​​"... the single most important cryptologic​​​​​​​breakthrough of the entire war."