Klim was the name given to powdered milk

Powdered milk

Powdered milk is a manufactured dairy product made by evaporating milk to dryness. One purpose of drying milk is to preserve it; milk powder has a far longer shelf life than liquid milk and does not need to be refrigerated, due to its low moisture content. Another purpose is to reduce its bulk for...

 rations issued by the International Red Cross to Allied prisoners in German captivity 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...

. The tins (klim tins) were reused for other purposes including piping fresh air into escape tunnels. The name is a simple reversal of the word milk.

Klim was also found in other theatres — for example in the Burma Campaign

Burma Campaign

The Burma Campaign in the South-East Asian Theatre of World War II was fought primarily between British Commonwealth, Chinese and United States forces against the forces of the Empire of Japan, Thailand, and the Indian National Army. British Commonwealth land forces were drawn primarily from...

, where troops retreating from the Japanese invasion found tins of Klim in deserted villages. These proved very useful and provided much needed sustenance.