Imagine a whole gang of Buster Keatons. The Keystone Kops could try to catch them, and great injuries and pratfalls would happen all around. Things would go bang. Masonry falling, people getting tossed around… And, of course, if it were made today rather than in the silent movie era, a lot of noise: police whistles, sirens, machine guns, screeching tires. And it would be a huge success. Like gangbusters.
Gang Busters was, in fact, a huge success. The true-crime-case radio show, which ran from 1936 to 1957, had exactly nothing to do with Buster Keaton or with the Keystone Kops, and was the perfect inverse of a silent movie: it was all sound and no vision. And such sound! The opening of each show featured a barrage of loud sound effects: police whistles, sirens, machine guns, screeching tires… By 1940, English speakers had taken this vigorous noise (and probably the great success of the radio show too) and mapped it onto vigorous being, and coming on like Gang Busters meant “doing really well.”
Which it has meant ever since, even though few people now know about the radio show; like gangbusters is by far the most common collocation for this word, and go (and going) and come on are the verbs that typically come before; go(ing) gangbusters is also common.
As to the overt sense of it, well, anyone can figure out what gangbusters means, and they won’t be wrong: “people who bust gangs.” When gangs were big news in the US – the roaring twenties, the dirty thirties – law enforcement officials needed to break them up and jail their members, and one who was successful at it (Eliot Ness is now the paragon) was a gangbuster. Not that they are a common vision of success now; the word seems to have taken on a life of its own such that a calling someone a gangbuster now would seem like a reference to the idiom.
And the word has the right sound and rhythm for a thumping success: three syllables, banging down the stairs like Buster Keaton, primary stress, secondary stress, unstressed, with the first syllable taking almost as long as the other two together, rather like the sound of something heavy hitting a floor and bouncing twice – or bouncing once and smashing across the floor on the second hit. The gang has a “bang” kind of sound, aided by the bursting b, and then the voiced stops with nasals give way to a voiceless fricative/stop pair /st/, like the the bouncing thing breaking, followed by the scattering sound of syllabic /r/. One is put in mind of James Brockman and Leonard Stevens’s song from the late 1920s, “I Faw Down an’ Go Boom.” Only in this case it’s a smashing success.
No need to stop just yet, though: gangbuster is a compound word. Gang comes from the verb gang “go,” as in Robert Burns’s “The best laid schemes o’ Mice an’ Men, Gang aft agley” – though Burns was no gangbuster where mice were concerned: “I wad be laith to rin an’ chase thee, Wi’ murd’ring pattle!” Anyway, gang (noun) refers to things that go together, and has more recently narrowed in sense to mean a nefarious group of persons. And buster is bust plus the agentive er; bust, in turn, is burst in an American vernacular alteration. Burst, like gang, is a good old Anglo-Saxon word, and it has always meant “break.” These days we think of it mainly as the kind of breaking that happens to things that go “bang” or “boom.” Which brings us back to Joseph Frank Keaton, who got his nickname Buster at a very young age from surviving a fall unscathed that an observer (Harry Houdini, in fact) reckoned could have broken bones. And it appears that he in turn was the original and source of the nickname and nonce-name Buster.