Traci Monteith is afraid of heights but she loves depths. She’s been diving in Vineyard waters for more than 10 years, but only recently has she been working toward certification as an advanced diver on the Oak Bluffs fire department dive team. On a recent Thursday evening, she wet-suited up alongside two other members of the team for their first night dive. As the sun set around them, they set their compasses to shore, secured airtight goggles to their foreheads and clutched their neon yellow flashlights, a new prop for the divers. One after another, they launched off the dock at the North Wharf at Edgartown Marine, flippered feet first into the 21-foot deep waters, careful to clear the dock behind them. Once they’d bobbed up and passed a quick equipment check, they pivoted their bodies and dove, head first into the murky waters, leaving only a fleeting swath of neon and a circle of bubbles in their wake. Minutes later, rings of bubbles appeared around the hull of a large boat docked in the adjacent spot.

For more than two years during a transitional period in the fire department ranks, the dive team’s training regimen lagged. But acting chief John Rose has made the dive team a priority in the last few months, and the team is poised to surpass the other town teams in training by the end of September. All 15 divers on the team, which includes seven new divers, should have their advanced open water certification by then.

“The new team is being very aggressive in their training and diving,” Mr. Rose said. Beginning July 4, dive instructor Heidi Raihofer has brought the divers on early morning, midday and evening training sessions like this one.

“If I want your attention, I will go like this,” Heidi said, shaking her own flashlight. The flashlight is one mode of communication for the divers, for whom underwater visibility is sketchy, especially under darkening skies. Each pair also received a line of twine for the purpose of learning how to conduct a systematic search underwater when eyesight isn’t reliable. Ms. Raihofer is a certified instructor and she trains all the town teams. She says she’s impressed with the time and dedication the volunteers devote to diving, taking time out of their busy summer work schedules to train. “Our fire departments on this Island are nothing short of spectacular,” she said.

When they emerged from the water, 45 minutes later, the divers dried off and headed for the showers. Among the items they’d recovered from the depths of the harbor were three flip phones circa 2004, bits of a terra cotta pot and two orange Crush bottles dated 1974. A small brown crab crawled out of one opaque bottle. But these pollutants aren’t the primary cause of the murkiness, said dive master Joe Leonardo; that comes from algae and other vegetation. The Edgartown harbor dates back to the 1600s, so the possibilities of treasure discoverable down there are endless. But treasure is just a perk of intense dive training. The firefighters are really there to familiarize themselves with diving equipment and procedure and learn lifesaving skills. Dives near and far from shore — including regular training at the Port Hunter wreck off East Chop — prepare divers to rescue or recover bodies and lost property from waters shallow and deep. There are eight new divers on the team this year, and seven or eight veterans, including William deBettencourt. Mr. deBettencourt has been diving for the fire department since the team began about 13 years ago.

Back then, the Oak Bluffs dive support team was the only one on the Island. All towns looked to it for rescues and recoveries. “As a fire department on an Island surrounded by water, it was something that was definitely needed,” Mr. deBettencourt said. (Since then, Edgartown and West Tisbury have developed their own teams.) In summer, boating and swimming activity increases exponentially on the Island, and much of it is concentrated around the town of Oak Bluffs. The town owns the largest harbor on the Island and the largest stretch of State Beach, which includes the jumping bridge — a popular but perilous spot. Vineyard Haven, which also has a highly active port, does not have a team, so Oak Bluffs divers are available to respond there when the need arises.

Unfortunately, many times when the team is called to the scene of an accident, rescue is no longer possible. Instead, the divers are called on to recover a body or lost property. “We have been out on rescues from jetties or distress calls, but most of the diving is from a recovery angle,” Mr. deBettencourt said. “It is what it is.” In the most traumatic cases, volunteers have had to recover people they know. “You have to have a good mindset for it,” Mr. deBettencourt said. “Not everybody is cut out for it.” While the Menemsha Coast Guard station is also available for dive missions, they are less accessible to swimmers in distress in Oak Bluffs waters and they only respond to ocean-side calls. “When somebody is in trouble in the water, we are their first line of resource,” Mr. Rose said. “We have a much quicker response time.”

Diving is expensive as a sport, but it’s even more costly as a public safety response. The most basic diving sets, which include suits, cylinders, flippers and regulators, cost upwards of $1,600, Ms. Raihofer said. For training this summer, dive team members have used Ms. Raihofer’s equipment. Chief Rose has increased the stipend available to divers this year, and is looking for ways to allocate funds in the next fiscal year budget to cover the costs of equipment. Until this year, dive team members had to purchase their own diving equipment. “All of them are community-oriented, and they are into public safety, and they have a drive to help others,” Mr. Rose said.

It’s not all sacrifice for the divers, however. They say they love the feeling of floating underwater. “It’s as close to weightless as you can be,” Mr. Rogers said. “It’s something that I would highly recommend.”

Eight members of the team share the same tattoo, inked into the skin of their forearm or calf, which they were inspired to get during a record year of water calls. It’s a Chinese design symbolizing honor and brotherhood. Teamwork is essential to their operations, Mr. deBettencourt said. “Nobody works better individually than you can as a team,” Mr. deBettencourt said. “You can overcome a lot more things.” Daniel Rogers, first lieutenant and another original member of the team, said the team is an opportunity to form bonds with people across companies and engines. “It brought a lot of different people together that wouldn’t necessarily hang out together,” he said.

The divers say steady support from Mr. Rose has raised morale and encouraged them to move forward. “He is somebody who has a lot of pride in the department,” Mr. Rogers said. “It’s nice to have it right from the top, to give that, whatever you guys need attitude,” he said.