At a very fast intensive speed or pace, as in expressions like, coming on like gangbusters or going like gangbusters. It is an Americanism dating from the late 1930s. The expression derives from the popular American radio series Gangbusters, which first went on air in 1935. Gangbusters were crime fighters and the radio series had a very striking sound intro consisting of police whistles, sirens, running feet, gunshots and machine gun fire. Within a very short while, the word was being used to describe anything fast, strident, enthusiastic or intensive.