Which is a phrase that was probably better understood in the '60s. Gang Busters was a radio series broadcast from the '30s through the late '50s, a show that dramatized real FBI cases like Dragnet did with police cases. It was infamous for its jarringly loud opening sequence, so the phrase "to come on like Gang Busters" was coined to mean coming on very forcefully.
That's fascinating, Christopher! Word and phrase etymology is an interest of mine!