The Enigma Code was quite important to victories in the Battle of the Atlantic and the intercepting of German intelligence. Project ULTRA, the group held responsible for cracking the Enigma code with 1.32 Trillian to 1 chance of success, was able to use the codes to successfully complete missions such as the landing in Italy off of North Africa, the success in the Battle of the Atlantic, the location of submerged submarines, and even the success of D-Day.

One example can be D-Day, being the largest scale battles of the entire war with almost 2 million US troops alone, entering the shores of Normandy. To ensure that Hitler's defenses were not located primarily at Normandy but further up, the plan to make the Nazi's believe the real intent of D-Day was further North in France was needed. Joan Pujol Garcia, a British double-spy (you can Wikipedia him), had even confirmed that the actual attack was not planned on Normandy. Hitler believed this account told. However, without the listening into Germany intelligence through a cracked Enigma code, it could not be confirmed.

Another example, Operation Mincemeat, allowed for the landing of Allied troops onto the coast of Italy. The plan was to drop a plane off the coast of Spain. Being neutral, the plane's components should not have been given to any side of the war. The Spanish, being Fascist, instead gave the plane to the Germans. Aboard the plane was an Allied soldier contained false documents cuffed to his wrist that stated the Allies had plans to use Greece as an entry point to take back the war effort in the West. The soldier was outfitted to look like a real human - given gum, a photo of a woman - anything that COULD make him appear as actually existed. He also needed to have been dead from drowning (bloating, etc). The Germans believed, CONFIRMED by intelligence gathered from messages sent through telegrams to which ULTRA's listeners could gather. This allowed for the landing on Italy.

While the German army was 'dwindling', the allies were not completely aware of this. In fact, the Germans only had enough supplies for 9 months (12 months at best!). The cracking of the Enigma was an intelligence success unlike any other with such a low success chance but with outstanding results.

Also note: the Enigma Codes are different per sector of the Third Reich. This means, while the Navy may have a certain set of codes PER DAY, the post office has another set PER DAY. Pure luck had it that the Nazis were lazy and did not change the codes every day. However, to ensure the codes were not changed, the allies had to 'not accept all information'. By this, the Allies had to allow soldiers to die - if every time a plan to attack failed, it would become obvious the Allies had the codes. Instead, as intelligence, you have to know which times you react to what you uncover.