The Finns perfected the design and tactical use of the petrol bomb. The fuel for the Molotov cocktail was refined to a slightly sticky mixture of gasoline, kerosene, tar, and potassium chlorate. Further refinements included the attachment of wind-proof matches or a phial of chemicals that would ignite on breakage, thereby removing the need to pre-ignite the bottle, and leaving the bottle about one-third empty was found to make breaking more likely.
As the cooling system was almost invariably placed where direct fire wouldn't hit them, the target of choice was the rear deck of a tank
; the burning contents of the bottle would pour through the large cooling grills and ignite fuel, hydraulic fluids and ammunition