The klim can ("milk" spelled backwards), was a round tin can that formerly contained powdered milk. Klim cans were approximately four inches in diameter and about three inches deep. Used in WWII, klim cans were supplied by the Red Cross for the prisoners. Klim cans were instrumental in the escape attempt from Stalag Luft III. The metal in the cans could be fashioned into a variety of different tools and other useful items such as scoops and candle holders. Scavenged klim cans were used in the construction of the extensive ventilation ducting in three tunnels that lead out of the prison camp. Former prisoner at Stalag Luft III, Charles Huppert became an expert in turning tin cans into tools. Huppert said, "We used Klim tins for everything that we made, because you could cut the ends out, and have a large piece of tin to work with. You can straighten that out flat, and make a...join them together in a locked joint, such as this, and take your wooden mallet and hammer them down. Then you take your backside of a knife and bear down on that, with a lot of pressure on both sides of that crimp, so that the tin will not separate, in order to make the tools that are used in the tunnels: the digging tools, the funnels, and the lamps to give light."
http://samilitaryhistory.org/vol086db.html (Illustration showing use of Klim and other tins for South African POW's "Blower" cooker)