In April, losses of U-boats increased while their kills fell significantly. Only 39 ships of 235,000 tons were sunk in the Atlantic, and 15 U-boats were destroyed. By May, wolf packs no longer had the advantage and that month became known as Black May in the U-boat Arm ("U-Bootwaffe"). The turning point was the battle centred on slow convoy ONS 5 (April–May 1943). Made up of 43 merchantmen escorted by 16 warships, it was attacked by a pack of 30 U-boats. Although 13 merchant ships were lost, six U-boats were sunk by the escorts or Allied aircraft. Despite a storm which scattered the convoy, the merchantmen reached the protection of land-based air cover, causing Dönitz to call off the attack. Two weeks later, SC 130 saw at least three U-boats destroyed and at least one U-boat damaged for no losses. Faced with disaster, Dönitz called off operations in the North Atlantic, saying, "We had lost the Battle of the Atlantic".