They trained for that scenario Monday, although 25 mph winds forced them to cancel the helicopter descent. But officers boarded the ferry Salish in seasickness-inducing swells that washed over the smaller police boats, King County sheriff's Sgt. Katie Larson said.
"It's dangerous," Larson said. "We've got to practice in the good and the bad weather, and at some point you have to weigh the risks," she said about canceling the helicopter drop.
The all-day training exercise, six months in the planning, involved up to 100 people from the Coast Guard, Washington State Patrol, King County sheriff's office and Seattle police in the waters between Vashon Island and Everett.
Two helicopters circled the ferry for a time as it was overtaken by two smaller Coast Guard boats, a sheriff's boat and police boats from Seattle and Bainbridge Island.
Despite the impressive show of force, the most important part of the drill is the cooperation and communication among agencies, Coast Guard spokesman Robert Lanier said.
"So we're all working on the same page if something were to happen," he said.
Officials have no reason to suspect the green and white ferries that ply their routes across the sound are targets, but they've received special protection since 9-11. The Washington State Patrol checks cars with bomb-sniffing dogs. The Coast Guard often escorts ferries with fast-moving 25-foot armed boats.
"I don't want to say it is a target, but we have to consider all threats, and this could be a threat," Lanier said.
Washington state operates the largest ferry system in the United States with 22 vessels on 10 routes, according to the state Transportation Department.
In another terrorism drill Sunday in Seattle, emergency fire and police responders from King, Pierce and Snohomish counties conducted a scenario of sarin gas being released on an Amtrak passenger train, said Fire Department spokesman Kyle Moore. Sarin gas is toxic and attacks the nerves.
Responders had to chase down suspects and decontaminate victims. They even had to figure out how they would decontaminate a suspect in handcuffs.
"If we had an event like this, it's going to involve multiple agencies," using different radio frequencies and procedures Moore said. "We wanted to test a unified command and working together," he said.