Brew up

From world war two and used, usually by British soldiers, to describe the effect seen when the amunition propellant in a destroyed tank starts to ignite. The flames shoot out of any opening, most usually the turret hatches, extremely violently, like a Roman candle. This terrified tankers and as a sort of black humour they referred to it as brewing up. Other nationalities sometimes referred to it as cooking off .. the ammunition was cooking off.