January 1929. Gangster Matt Malloy walks into a sporting goods store; he can't buy an automatic pistol without a police permit, however anyone with $150 can buy a machine-gun. Later, at the Club Montmartre, half a dozen choppers are laid out on Nitti's table. The Council says that now they can move in on the Northside and Bugs Moran. Nitti picks up a chopper and says, ""You got 'em-- use 'em!"" Gang war!

Chicago. Right after the St. Valentine's Day Massacre. (February 14, 1929.) Ness and his men are scouring Chicago, looking for Bugs Moran.  Ness says there used to be 2 gangs in town, now there's just one.  Ness figures if they get to Moran first, maybe he'll talk-- he might just be mad enough to give them the information they need.