I first learned of the bombings yesterday when my airplane touched down at Reagan National. Several breaking news alerts popped up. About 21 minutes after the blasts, I clicked open one of the many iPhone apps that streams in the radio feeds from Boston's police, fire, and EMS departments.

You can listen to the first 24 minutes of the police department response here. A supervisor, Delta 9-8-4, was on the scene of the second explosion immediately. His instinct: Clear an adjacent road for ambulances. "All officers, watch for secondary devices."

The Fire Department's audio — an engine company reports an explosion at 671 Bolyston Street — is here. "We have reports of two explosions here; we have at least a dozen people with serious injuries." Tower 17 was the first truck on scene. "We have a mass casualty," the dispatcher responds. Within three minutes, the dispatcher had secured a route for the paramedics to get to the scene and a chief was warning of secondary devices. "Fire alarm" is the dispatch center.

The "UCC" refers to the joint police, EMS, fire, and emergency response command post.

Here are several longer versions of the scanner audio as recorded by hobbyists.

The police department brass use the call-sign pre-fix "Yankee," and whenever someone with a "Yankee" in their name is on the air, you know that something major is happening. The dispatchers, commanders, and officers were organizing the chaos, but already, they were internally organized. A universal command center had been set up quickly; one dispatcher was in charge; one chief was in charge; orders were funneled up and down the chain. Boston uses relatively few frequencies for its special operations, and though this means that they could easily get clogged, it also makes it easier to communicate with everybody. 

Within a half hour, on the detective channel, the "Victors" — the detectives — were gathering at a point. On the main channel, a senior officer was handling the requests for EOD canines, a half dozen of which had just arrived from nearby jurisdictions. 

It did seem as if the department had rehearsed for something like this, and indeed, I learned later that they had. The FBI and various Boston agencies have practiced responding to major mass casualty events.  

When I was in college, I would spend many a weekend afternoon sitting on a bench outside a fire station in downtown Boston, listening to the station scanner and trying to get through my history reading. The bench was positioned between two large bays, and so when a "box" was struck and the fire apparatus were dispatched, they would pass by me on both sides, deafeningly, screamingly loud, a blaze of red. I found it exhilarating.