Question

What did the United States use to overcome the threat of German U-boats?

Answer 1

Mainly the Convoy System of sailing through the North Atlantic.

Explanation:

The Convoy System consisted in grouping merchant, tankers and freight ships into groups that could be protected by few and well placed patrol boats (such as corvettes or frigades).

It was impractical and basically impossible to disperse the ships and protect each one of them due to the small number of armed patrol ships.

Another and probably decisive weapon was intelligence: by decrypting German Navy orders to the Wolf Packs of U-boots it was possible to steer the convoys away from the hunting zones leaving the U-boots without preys and possibility to reach them (due to their low velocity in particular when immerged to avoid detection).