After Doenitz pulled his U-boats away from the North Atlantic convoy route, his plan was to use his U-boats in more distant areas. The obvious lack of success against the convoy system needed to be overcome. Until a way could be found to beat the combination of aircraft and radar, the convoys would have to wait. Doenitz's plan meant long transits to on-station areas and, if any success was to be forthcoming, long stays in the operating area. In order for this to work, the U-boats would have to be refuelled in mid- Atlantic. The area around the Azores was a major refuelling area in the summer of 1943. Doenitz's program for refuelling his U-boats was extremely ambitious. Because of stepped up operations in the spring of 1943, three or four refuelers were on station at all times. The remainder were either enroute to or from port or in port for servicing. The margin for losses was obviously slim. Thus, when the US Navy carrier task groups began sinking the precious refuelers, the entire U-boat force was affected. Destruction of the refuelers reduced the standard U-boat to a much restricted operating radius. Because the refuelling fleet was small, great care was taken to protect it. The refuelling rendezvous was carefully chosen. The positions were usually picked in mid-ocean well away from convoy routes and outside the range of Allied patrol aircraft. All U-boats approaching a rendezvous were directed to maintain radio silence unless it was absolutely necessary to break it. In addition, combat U-boats were to consider themselves expendable by remaining on the surface to fight while the refueler dove in event of a surprise attack
