This battle began to keep Allied shipping lanes open because around July, 1940, German U-Boats bagan attacking merchant ships that were sailing across the Atlantic. The Allies biggest problem was that their coastal patrol aircraft couldn’t fly across the ocean, making their ships vulnerable and the Germans superior in the seas. In 1941, the Germans sunk 2.9 million tonnes of allied cargo and the following year, 6 million tonnes. The Allies soon found their solution; corvettes. Small, inexpensive ships originally designed to patrol the Canadian coast but now, they’d be guiding the vulnerable merchant ships across the Atlantic, armed with torpedoes, anti- aircraft guns, and deck guns along with listening devices to detect the German U-Boats.