Until 5734/1974, few people knew  about an operation that was so secret  that it was labeled not “TOP  SECRET” but “ULTRA SECRET.”  This was Britain’s “Ultra” cryptanalysis  project that, during World War II,  secretly cracked Germany’s secret  codes, laying bare many of the Nazis’  military secrets for six years until  their defeat in 5705/1945. In  5763/2003, it was reported that Winston  Churchill apparently told King  George VI, “It was thanks to Ultra  that we won the war!”
One of Ultra’s first tasks was to  prevent Field-Marshal Erwin Rommel  from sweeping through Egypt into  Palestine. 
Although most military information  during World War I was gleaned by  low-flying aerial photography and  trench raids, during this war the age of  radio espionage began: listening in to  the enemy’s radio messages. To  counter this, each side used codes and,  to counter the codes, each side set up  teams of cryptographers to cipher  them.
Since shortly after World War I, the  Germans had been developing a code making  machine, called Enigma,  dreamt up by German inventor, Arthur  Scherbius. They regarded it as  impregnable. Basically, a typist would  feed the letters of a message into this  machine, which then spat out a version  of the message so permutated  that it was estimated it would take top  mathematicians a month to work it  out. And, by then, it would be too late  because the permutations were regularly  altered. Another machine, known  as FISH, worked along similar lines.  German cryptanalysts were convinced  that their machines were impregnable.  They were wrong.
By 5792/1932, the Polish were  beginning to crack the Enigma codes  and, shortly before World War II, a  Polish mechanic, hired by a German  factory, helped Polish intelligence  build their own working model of the  Enigma machine.
To crack the codes, the British set  up the “Government Code and Cipher  School” at Bletchley Park, fifty miles  north of London, and staffed it with  chess experts, mathematicians and  pioneer computer scientists, including  Alan Turing, one of the fathers of  modern computing.
This last group of people was  essential because even the fastest  human brain would take weeks to  work through the Enigma’s tens-of-thousands  of permutations. Thus the  computer age was born just in time to  stop Germany in its tracks.
The Polish had already invented  electro-mechanical machines, or early  computers, known as the Bomba, and  the British used a different, far superior  version, called the Bombe, eventually  producing about 200 of them.  The Bletchley Park operations were  kept so secret that their results were  taken directly to the Prime Minister,  Winston Churchill, in a locked box  which he personally held the key to. 
One of the first big success stories  of Bletchley Park was its role in  defeating Rommel at the second Battle  of El Alamein, upon which the  future of the Jewish yishuv in Palestine  hinged. In general, Rommel’s  forces were better trained, some of  their weaponry was superior, and  Rommel himself was famed as a  superb strategist. The key to destroying  him was to destroy the mobility of  his fearsome Panzer units, and the key  to doing that was to dry up the convoys  of petrol coming over the  Mediterranean from Italy. The same  applied to the availability of ammunition  and spare parts.
This is where Ultra came in. Well  aware that everything depended on his  petrol supply, Rommel sent a constant  stream of pleas by radio, which was  picked up by Ultra. In reply, Rommel  was radioed back, and told when and  where to expect his next shipments.  Thus the Allied navy and air force  knew exactly where to pick off the  Germans’ helpless tankers at sea. The  only problem was not making it obvious  that the Enigma code had been  cracked.
To achieve this, the Allies had a  strict rule. No tanker or cargo ship  was ever sunk before it was “spotted”  by a reconnaissance aircraft or submarine.  “Both Admiral Cunningham and  Air Vice-Marshal Sir Keith Park, the  Air Force officer commanding Malta,  were meticulous in sticking to the  security rules for Ultra. They took  great care to make absolutely sure that  each convoy had duly seen the aircraft  that was sent up and was supposed to  have spotted it before the Navy turned  up. Park would order an aircraft just  close enough to where he knew the  convoy would be for it to seen by the  ships. Then, a little while later, the  Navy would arrive and send all the  ships to the bottom” (“The Ultra  Secret” by F. W. Winterbotham).
The ethical dilemma of Ultra was  that, to keep the Germans from realizing  what was going on, it was sometimes  necessary to sacrifice people’s  lives. On one occasion, for example,  an Allied pilot sacrificed his life to  keep up the ruse.
“There was a patchy fog in the  Mediterranean and, this time, the  Malta aircraft couldn’t find the convoy,  which had evidently changed  course as an extra precaution. The  pilot of the RAF (Royal Air Force)  spotter plane, unable to find the ships  through the fog patches, cruised  around in these dangerous skies until  suddenly, through a small break in the  fog, he saw them on a different course  to the one that had been given. It was  virtual suicide for a single British aircraft  to send a signal from the air…  since the Germans in Sicily would be  able to get a fix on his position and  enemy fighter aircraft would be sure  to intercept him before he could get  home. But the courageous pilot  reported the convoy’s position and  paid for it with his life” (ibid).
Because the pilots and seamen  always knew exactly where to search,  the Germans assumed that the Allies  had 400 submarines prowling the  Mediterranean when, in reality, they  only had 25. Similarly, they assumed  that Britain had a huge reconnaissance  air force on the Mediterranean island  of Malta, when all the RAF actually  had stationed there were three airplanes!
Thanks to these tactics, over 40 percent  of all the Axis’ ships carrying  supplies to Rommel were sunk, and  60 percent were sunk just before the  Battle of El Alamein.
Thus, shortly before the battle that  broke out in October 5702/1942,  Rommel desperately appealed to  Hitler’s Headquarters:
“The German troops of the Panzer  Army in Africa, who are bearing the  brunt of the war in Africa against the  finest troops of the British Empire,  must be provided with an uninterrupted  flow of the supplies essential for  life and battle, and every available  ship and transport aircraft should be  employed for that purpose. Failing  this, the continued successful maintenance  of the African theatre of war  will be impossible and army will,  sooner or later, run the danger, when  the British launch a major offensive,  of suffering the same fate as befell the  Halfaya garrison (that was  destroyed)” (The Rommel Papers).
Subsequently, when the battle of El  Alamein broke out, it was basically  lost before it began. Without adequate  petrol, Rommel could not execute his  famous desert maneuvers that had  bedeviled the Allies for the past two  years. As he recorded:
“We still could not take the risk of  putting the main weight of our  defense on to operations in the open  desert, for the following reasons:  “(a) The relative strengths in  motorized divisions had become too  unequal. While our opponents were  receiving a steady flow of motorized  reinforcements, we received only  non-motorized which were as good as  useless in the open desert… (b) The  British air superiority… (c) We were  permanently short of petrol. I did not  want to get myself again into the awkward  situation of having to break off a  battle because we were out of petrol.  In a mobile defensive action, shortage  of petrol spells disaster” (ibid).
General Claude Auchinleck, a commander  of the British forces at the  time, conceded that, if Rommel had  not been strangled of supplies, the  Germans could have broken through  to Egypt. 
An equally important role played  by Ultra was helping overcome one of  the greatest threats of World War II,  Hitler’s U-Boats, which threatened to  cut off supplies from America. By  deciphering radio messages to submarines,  the Allies could locate them  and send their convoys on alternate  routes.
By early 5703/1943, the British had  perfected the world’s first programmable  computer, that they called  Colossus, in order to crack the German  codes. Because this top secret  was only declassified late in the  5730s/1970s, people thought for  decades that the first programmable  computer invented was the ENIAC,  developed in the University of Pennsylvania,  some time afterwards.
By this time, the Allies were intercepting  up to 2,000 messages a day,  some of them from Hitler himself.  Other German codes, such as the Triton,  were also routinely intercepted  and analyzed.
As mentioned earlier, the “Ultra”  was kept officially secret for 29 years  until 5734/1974. The British  destroyed their ten Colossus computers  in the early 5740s/1980s, but one  of its designers, Tommy Flowers,  reconstructed an exact copy in  5754/1994. By today’s standards, the  Bombe and the Colossus were primitive  but, in their time, they helped  spell the difference between victory  and defeat.