Groton — It's an unlikely scenario, but still one the Naval Submarine Base must prepare for.

The package store on base receives an order and on the pallet with the regular shipment is a box, addressed to the commanding officer, which is emitting a white powdery substance and has a biohazard symbol on it.

An employee at the package store calls 911 and reaches the dispatch center now based in Norfolk, Va., which alerts first responders here to the situation. Security and fire personnel on base are sent to the scene. Other area fire departments and emergency personnel are put on standby. An announcement goes out over the base's notification system, known as the Giant Voice. And base personnel receive text alerts notifying them to shelter in place.

Base personnel tested their hazmat response Thursday morning as part of annual training drills being carried out at all U.S. Navy installations.

"This annual exercise is designed to enhance the readiness of Navy Security Forces and ensure seamless interoperability among the commands, other services and agency partners," according to a news release from Navy Installations Command.

Throughout the exercise, base personnel are training for a variety of scenarios, from an active shooter inside the gates to an attack on the waterfront.

Thursday's drill tested "our muscle moves that we aren't normally practicing," said Capt. Paul Whitescarver, commanding officer of the base. The chances of this kind of hazmat emergency happening on base are "pretty slim," he said, adding that his biggest worry is still an insider threat.

As Whitescarver explained back in 2016 when the base was going through the same exercise, "Can I defend against a person who shows up at a gate with a gun? Yeah, because I can shut my gates," he said at the time. "But a person who's disgruntled inside the fence line, that's tough."

In the package store Thursday, two base firefighters dressed in hazmat suits and masks do a quick reconnaissance. They take an initial sample of the white powdery substance. Meanwhile, the package store employee is being evaluated outside. "He's not showing signs of diminishing health," an official reports over his radio.

Base fire Chief Thomas Clapsadle Jr. said it's a job requirement for his 44-member department to be trained as hazmat technicians. Before 9/11, the base's fire department had the only hazmat team in the region, according to Clapsadle.

Outside the package store, base officials activate the Emergency Operations Center, or EOC, in a separate building. That's where Whitescarver and other base leadership are stationed to monitor the situation.

"The more we train together, the better we get," said David Cruz, installation training coordinator, describing how the drill tested coordination among a number of different personnel.

After the drill was over, officials gathered at the EOC to discuss how to improve the response. There was talk of making sure contractors are informed of proper protocols in the event of a hazmat situation, and concern that it took 10 minutes to activate the EOC.

j.bergman@theday.com