Why did 1942-1945 nickels contain silver?

"War nickels" were made of an alloy of copper, silver, and manganese to save nickel for the war effort. The alloy gave the coins the same weight and magnetic characteristics as their copper-nickel counterparts so they wouldn't cause problems with devices such as counters and vending machines.

At that time silver's price was controlled at $1.29/oz. The tiny amount (1.5 gm) in a war nickel was worth about 5 or 6 cents. Today (2012) it's worth about $1.25