Black May (1943) - AbsoluteAstronomy.com

‘Black May’ refers to a period (May 1943) in the Battle of the Atlantic campaign during World War II

World War II

World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

, when the German

Kriegsmarine

The Kriegsmarine was the name of the German Navy during the Nazi regime . It superseded the Kaiserliche Marine of World War I and the post-war Reichsmarine. The Kriegsmarine was one of three official branches of the Wehrmacht, the unified armed forces of Nazi Germany.The Kriegsmarine grew rapidly...

U-boat arm (U-Bootwaffe) suffered high casualties with fewer Allied ships sunk; it is considered a turning point in the Battle of the Atlantic.

After February battles around convoys SC 118

Convoy SC 118

Convoy SC-118 was the 118th of the numbered series of World War II Slow Convoys of merchant ships from Sydney, Cape Breton Island to Liverpool.-Prelude:...

, ON 166, and UC 1, Black May was the culmination of the March thru May 1943 crisis in the Battle of the Atlantic.
March had seen the U-boat offensive reach its peak, with a series of major convoy battles, first around convoys HX 228

Convoy HX 228

HX 228 was a North Atlantic convoy of the HX series which ran during the battle of the Atlantic in World War II. It was one of 4 convoy battles that occurred during the crisis month of March 1943 and is notable for seeing the loss of the Escort Group leader Cdr AA "Harry" Tait.-Prelude:HX 228 was...

, SC 121, and UGS 6; then followed the battle for HX229/SC122

Convoys HX.229/SC.122

The battle around convoys HX 229 and SC 122 occurred during March 1943 in the Battle of the Atlantic, and was the largest convoy battle of World War II. British merchant shipping was formed into convoys for protection against...

, the largest convoy battle of the war.

Allied losses for March totalled 120 ships of 693000 LT (704,122.7 t), of which 82 (476000 LT (483,639.8 t)) were lost in the Atlantic.