When the 1991 Halloween Nor’easter — the “Perfect Storm” — swept up the coast of New England 20 years ago, Ruben Colon was 13, living in San Juan, Puerto Rico, far away from Maine’s unforgiving coastal waters.

But now, as a boat coxswain for the Coast Guard, he knows that when the next big storm occurs, he and his crew will be on the front line, saving lives and property.

“We’re a heavy-weather station,” said Colon. “That’s what we do.”

Colon and his crew work out of Coast Guard Station South Portland, across the harbor from the bustle of the Portland waterfront. The station is part of Coast Guard Sector Northern New England, which is responsible for more than 5,000 miles of coastline.

The sector mounted dangerous rescue operations for the October 1991 storm that savaged the New England coast, sinking a fishing boat from Gloucester, Mass., with its crew on board. The storm was chronicled in a best-selling book and movie that cast a spotlight on Linda Greenlaw, the Maine swordfishing boat captain who rode out the storm.

The Coast Guard operates six rescue boat stations in Maine, one in New Hampshire and one on Lake Champlain. It launches an average of more than 600 search and rescue missions in the sector a year.

South Portland is home to vessels that include two 47-foot motor lifeboats, the workhorses of the Coast Guard’s coastal rescue boat fleet. The almost unsinkable boats can weather hurricane-force winds and heavy seas. If the boat should capsize, it can right itself in less than 30 seconds with all equipment fully functional.

“They’re built to withstand about as extreme conditions as people can withstand,” said Lt. Nick Barrow, chief of the command center for Coast Guard Sector Northern New England.

The vessels are the ones that regularly respond to rescues in the rapidly changing conditions in Casco Bay.

“A mission might start out fairly easy,” said Boatswain’s Mate Second Class Jon Gielarowski, a former lobsterman from Brooklin. “But it can change quickly, and we have to adapt and overcome the new challenges.”

Tides, weather and a host of other conditions can make any rescue difficult.

“Every case has its own challenges and personality,” said Colon, recalling a rescue where rising tides called for quick decisions to keep a hunting party from being swept up and over a ledge to which they clung after their boat was smashed on the rocks.

Most rescues occur in the summer, when recreational boaters flock to the area. The numbers drop with the arrival of autumn.

“When winter comes, the number of search and rescue missions goes down,” said Barrow, “but the consequences go up.”

Should an unprotected person go in the water, he will rapidly succumb to hypothermia, and rough weather and chill waters can put the lives of both those in distress and their rescuers at risk.

Such concerns play a vital part in the complex judgment calls that are made by all involved in each search and rescue mission. In the back of everyone’s mind is the knowledge that no one gets helped when the rescuers require help themselves.

“When it comes to putting boats in the water and launching aircraft, it’s critically important that we manage risk,” said Barrow.

An old motto of the U.S. Lifesaving Service — a precursor to the modern Coast Guard — was “you have to go out, but you don’t have to come back.”

Times have changed.

“You have to go out, and you have to come back, and you have to bring your boat and plane back with you because we’re going to need them and you tomorrow,” said Barrow.

Still, search and rescue crews will launch in situations that would leave most people shaking their heads and the Coast Guard’s principle of on-scene initiative leaves many of these decisions in the hands of the rescue crews themselves, allowing them to judge the level of risk.

“We go out and take care of business,” said Barrow. “We often accept high risk when there’s high gain.”

But it’s not only real emergencies that challenge the crews.

One vexing situation for the search and rescue crews in Maine is the number of drifting kayaks and other small boats that get reported to the Coast Guard. Each drifting boat comes with the assumption that there is also a boater in the water, in need of help, until it can be proven otherwise.

That means that search and rescue crews are launched and sometimes aircraft are dispatched to aid in the search. The costs of such operations can reach many thousands of dollars. Too often it turns out that the boat was simply poorly secured and drifted off with a rising tide.

“So many times it’s a false alarm,” said Colon. “But when it’s real, it’s so satisfying.”

Since the Coast Guard operates with limited resources, and boats and cutters might not be nearby in rescue situations, it will often work with the help of outside agencies, such as the Maine Marine Patrol, to get help on the scene as soon as possible.

Another tool in its arsenal is the Urgent Marine Information Broadcast, a radio call to all mariners in the area alerting them that there is a vessel in distress, where it might be located, and asking them to help, if possible.

Often professional fishing boats are first to arrive.

“It’s a close community,” said Colon. “Once we send out a call for help, some 50 percent of the time fishing boats get there first. It’s pretty impressive when you see it.”

For Colon and his crew, there is more to the day than waiting for a rescue call. Their missions also include port security, drug interdiction, enforcing fishing laws and responding to oil spills, to name just a few.

It means that a crew may go from an everyday safety inspection, to escorting a large cruise ship into Portland Harbor, to being called to respond to an overturned boat in Casco Bay.

“That’s part of our multi-mission mandate,” said Gielarowski. “We’re jacks of all trades. One day you’re doing fisheries inspections, the next you’re escorting the first lady.”

And while a newer version of the Perfect Storm hasn’t hit yet, the crew of Coast Guard Station South Portland and its counterparts throughout New England are prepared for when — not if — the next major storm comes.

“You’re always waiting for the big one,” said Gielarowski.