Atlantic, Battle of the (1939–1945) Ships than even an expanded U-boat fleet could sink, with construction averaging three months per ship and 1,500 ships per year at its peak U.S shipyards alone were also turning out 200 escorts per year, which subsequently sank more U-boats than Germany could build or crew But not all that was clear to either side until mid-1943 A new Western Approaches commander, Admiral Max Horton, organized hunter-killer groups of ASW aircraft, escort carriers, and fast escorts as greater supplies of each weapons system became available More U-boats failed to return to home ports as a result Also notable were pioneering ASW tactics developed by Royal Navy Captain John Walker, first in his role in convoy escort duty then as commander of Second Support Group This new offensive-mindedness was approved by Allied leaders at the Casablanca Conference (January 14–24, 1943) Five full Support Groups, each with at least one escort carrier, were now formed to take the fight in the Atlantic to the U-boats Where escorts previously sought to suppress U-boats while their convoy steamed away, Support Groups instead steamed at flank speed toward any convoy that reported U-boat action They then remained in the area to hunt down and kill the enemy, long enough that he could no longer stay submerged or actively driving him to the surface or sending him to the bottom An Atlantic Convoy Conference, held in Washington in March 1943, redistributed area responsibility among the three major navies The RCN assumed control of convoys north of New York and west of 47° longitude, the USN henceforth made its major effort farther south, while the RN controlled the Western Approaches and home waters German production meant that Dönitz just then achieved his “decisive” 400 U-boat fleet The protracted, climactic phase of the Battle of the Atlantic thus took place from January to July, 1943 A record 170 U-boats were actively deployed in March, attacking 11 convoys and sinking numerous merchantmen But most convoys got through to Britain unsighted by any German, while improved ASW tactics took a count of 15 U-boats Such attrition of experienced crews and skippers could not be borne for long by the Kriegsmarine More U-boats went down in April, while 40 boats were lost to Dönitz in May In return, just six convoyed merchantmen were sunk The losses included Dönitz’s younger son He would lose his eldest son in the silent service later in the war Otherwise, he seemed unconcerned with crew losses in anything but operational terms, and they had become unsustainable Dönitz ordered an end to attacks on northern convoys in the late spring of 1943, shifting most boats to concentrate on less well-defended routes He admitted at least temporary defeat and recalled all U-boats from deep Atlantic operations on May 23 The Battle of the Atlantic had been won by the Allied navies and sailors of the merchant marine, even though it was far from over, which is essentially what Winston Churchill told the House of Commons on September 21 In a climactic four month period from April to July, 1943, 109 U-boats had been sunk Many succumbed to aircraft patrolling the Bay of Biscay; others fell to powerful surface Support Groups and increasingly confident and numerous Escort Groups U-boats sank just two ships in the North Atlantic in August, even as Allied warship strength markedly increased By mid-1943 the USN alone operated four Support Groups 92