 On March 10, 1943, the Germans added a refinement to the U-boat Enigma key, which blinded the Allied codebreakers at Bletchley Park for 9 days.That month saw the battles of convoys UGS 6, HX 228, SC 121, SC 122 and HX 229.One hundred and twenty ships were sunk worldwide, 82 ships of 476,000 tons in the Atlantic, while 12 U-boats were destroyed.