Answer:
Technology, convoy system, Ultra, use of Aircraft, Iceland, mass production of ships, Lend Lease, and a strong effort to win.
Explanation:
Technology: Radar, Sonar and radio direction finding or Huff-Duff, depth charges all advanced significantly and aided the finding of Submarines.
Convoy System: The British instituted the Convoy System at the start of hostilities based on their bad experience in World War 1. The Americans on the Eastern Seaboard did not start convoy system right away and paid the price.
Ultra: The Ultra Secret that the British were able to read much of the wireless communication of the Germans made a significant difference. The British gave a lot of credit to Huff-Duff and other deceptions to cover this.
Aircraft: Long range air patrols and Carrier based aircraft harried German Submarines and sank many.
Iceland: The British invaded Iceland in May 1940 and handed over to the Americans later. The air bases, radar sites and ports all helped the war effort even though Iceland technically was neutral throughout the War.
The American mass production of Liberty Ships helped replace ships faster than than they could be sunk.
Lend Lease made 50 older destroyers available to the British early in the war.
Churchill worried a lot about the Battle of the Atlantic and he gave it considerable attention motivating others.
