The Battle of the Atlantic, lasting the entire war, involved naval conflict, often between German submarines and American and British shipping. The Germans deployed U-boats as their primary weapon and used them against British, American, and other allied vessels. The first few years of the campaign saw tremendous victories for the Germans, who were able to sink allied shipping, which was not yet using the convoys, with impunity. When the allies began using convoys, the Germans changed their tactics from sending out individual submarines to cover a certain area or roam until they found a target to gathering several U-boats together in a “wolf pack” and attacking whole convoys at once.