When officer James (Jamie) Craig, the hands-on-hips 26-year veteran of the Edgartown police force enters a room, he doesn’t think much about the decor.

He thinks about the floor plan. He thinks about lines of sight. He thinks about the doors, stairs, windows, locks, lighting and even light switches. Most importantly, he thinks about the quickest way he can get out.

“If you’ve been doing this stuff as long as I have, then that’s just the way you think,” Mr. Craig said. “It’s normal for me. And it should be for you, too.”

Mr. Craig isn’t just speaking hypothetically. The former Navy helicopter pilot who has served two active tours of duty — one in Iraq during Operation Desert Storm, another in the Adriatic during the Bosnian civil war — is using his military expertise to lead active shooter training sessions for organizations throughout the Island. He’s taught librarians, reporters, teachers, and yes, every Island police department, what the best-practice protocol is for the still unlikely, but increasingly common scenario of engaging with a live gunman.

“I never like to say that the Island is magical and different with rainbows and unicorns,” Mr. Craig said. “It isn’t. Bad guys go on vacation too.”

During the training sessions, Mr. Craig teaches people about the importance of preparing for the unpreparable — a process that begins with conceiving the inconceivable. He explains that places like Parkland and Squirrel Hill, where two recent mass shootings took place, were rated the safest neighborhoods in their regions. Mass shootings occur almost every day in the United States, he says, and nearly a quarter of them occur at Wal-Mart. He has his trainees listen to a 911 call from the librarian at Columbine High School and watch testimony from a survivor of the Virginia Tech shooting. He waxes rhapsodic about OODA (observe-orient-decide-act) loops and cerebella, emphasizing action over inaction, decision over indecision. He illustrates the importance of locating all entrances and exits by showing graphic footage from the Station nightclub fire in Rhode Island.

It’s shocking. It’s eye-opening. And it’s scary.

But it works.

“Training allows you to stress innoculate,” Mr. Craig said. “It’s just compartmentalization. It’s a skill set you have to develop, where you go into something and you have 30 worries and you just put 25 of them in a box. And you say, right now, my focus is going to be getting through that door. That’s what it’s going to be. And when you’re that hyper-focused, you don’t feel scared.”

Mr. Craig knows that most people don’t want to think about a potential active shooter scenario, let alone train for it. To him, that’s why it’s so important.

“I hate that we live in a world where this is happening,” he said. “But it’s basically daily, and we’ve become desensitized to it . . . I have a small little role to play in American law enforcement, and all it can be is just trying to help train people to do the best job they can in a scary situation. So I think the training is really necessary.”

Along with the active shooter training sessions, Mr. Craig also heads the Island’s voluntary, interdepartmental tactical response team. The part-time SWAT group arose about 10 years ago out of Mr. Craig’s experience loading Marines and Navy Seals into helicopters during battle operations.

“There was a need to have an indigenous tactical response team on this Island,” Mr. Craig said. “Because there was a misconception among the police chiefs that the cavalry is going to come . . . but I know how long it takes to put that together. You just can’t expect a SWAT team from the Cape to jump in a helicopter and come over. I told them I would do everything, and they were like, sure, go for it.”

The team was trained by the Los Angeles police department and requires a physical fitness test, a firearms test and an interview. Although Mr. Craig prefers “operators, door kickers and trigger pullers,” he also has three negotiators, one tactical medic and two tactical support officers. He teaches the supreme importance of synergy, teamwork and knowing your fellow officers. When the Boston Marathon Bombing occurred, Mr. Craig’s team was one of the first ones called.

“This isn’t Martha’s Vineyard SWAT light,” Mr. Craig said.

They undergo double the state-mandated firearms training, practicing shooting at night and from the windows of high-speed cars. Part of that firearms training also means learning when not to shoot.

Mr. Craig described a “suicide-by-cop” situation that occurred in Vineyard Haven this summer.

“He was provoking someone to kill him, and our job is to bring everybody home safe,” Mr. Craig said. “The tactical response team is why he didn’t get killed. He got tased. And my understanding is that when he got through his crisis moment, he went, ‘oh my God, thank God they didn’t kill me because I was having a manic episode.’ Because if we shot that guy, nobody in the police world would have said we did the wrong thing.”

Mr. Craig has long been obsessed with analyzing performance in high-pressure situations. His hero growing up was Neil Armstrong — not for being the first person to land on the moon, but for his storied career as a Navy helicopter pilot. He reads police reports and survival stories in his spare time. He’s mission-focused and goal-oriented, with few career ambitions outside of his duties as an officer.

“That’s one of the reasons I’ve focused my career on tactical operations,” Mr. Craig said. “I’ve never wanted to be a detective, because I think that would be too frustrating. But tactical operations is a little more cut and dry.”

He also writes, a skill he inherited from his father Philip Craig, a renowned Island mystery novelist, Wheelock College English professor and Iowa Writers Workshop graduate.

The irony is not lost on Mr. Craig that the son of a mystery writer wants nothing to do with detective work.

“He’s my writing inspiration, but not my policing inspiration,” he said of his father. “Although several things I told him about my job made it into his books unbeknownst to me, and I’d be like, ‘Dad, I kinda said that to you in confidence. But okay.’”

One of the participants in Mr. Craig’s active shooter training session at the West Tisbury library was a former student of his father’s at Wheelock.

“She came up to me afterward and said, you teach exactly like your father,” Mr. Craig said. “She said, you sound like him, your mannerisms are just like him. So I probably adopted a lot from him. And definitely my interest in teaching.”

Even outside the classroom, he doesn’t shy away from teachable moments. During his early days as a police officer, he brought in a kid who tried to buy liquor as a minor and gave him “one of his horrible lectures.” For the next 25 years, the kid would come back to the Island in the summer, find Mr. Craig on the street, and thank him for the speech. He introduced Mr. Craig to his wife, children and business partners.

“He’d tell them all,” Mr. Craig said, “‘This is Officer Craig. You have to meet him. When I was hanging out with the wrong people and doing the wrong things, he gave me this talk. I attribute my success in life to him turning me around.’” It’s clear, too, that a little bit of Officer Craig must have rubbed off on his father. Before Philip Craig died 11 years ago, he dedicated one of his last books about a fictional Island police force, Murder At A Vineyard Mansion, to the ones who serve as their flesh and blood inspiration. The dedication reads: “For the real police officers / on the real Island of Martha’s Vineyard / who protect and serve and stay human while doing it.”

Mr. Craig is one of those real police officers, and it’s his job to convince people that this Island isn’t a fantasy land. The harder part is staying human while doing it. But that too is why he’s here.

“I’ve been to 49 countries on four continents,” Mr. Craig said. “Having been a lot of places, and done a lot of things, it’s comfortable. It’s like putting your feet up by your favorite fire. I’m home.”