From mid-June 1943 the technological and industrial superiority of the Allied navies allowed the Americans, Canadians, and British to form hunter-killer groups consisting of fast anti-submarine escorts and aircraft carriers. The purpose of naval operations changed from avoiding U-boats and safeguarding convoys to seeking them out and destroying them where ever they operated. USN hunter-killer groups operated throughout the Atlantic. Argentia had been an important base for the naval taskforces until superseded by the Royal Canadian Navy in early 1943. U-boat operations were "crushed" by these task forces: 14 were sunk and only two of seven crews operating in Brazilian waters returned to Germany.