Dönitz was content that he now had the naval power to extend U-boat operations to other areas aside the North Atlantic. The Caribbean, Brazilian waters with the coast of West Africa designated operational theatres. Waters in the southern hemisphere to South Africa could also be attacked with the new Type IX submarine. The strategy was sound and his tactical ideas were effective. The number of boats available allowed him to form Wolfpacks to comb convoy routes from east to west attacking one when found and pursuing it across the ocean. The pack then refuelled from a U-boat tanker and worked from west to east. Raeder and the operations staff disputed the value in attacking convoys heading westward with empty cargo holds. The tactics were successful but placed great strain on crews who spent up to eight days in constant action.