Offshore lighthouses presented unique challenges for their architects, builders and keepers. Jeremy D'Entremont profiles these iconic structures in his new book, “Wave-Swept Lighthouses of New England,” released by Arcadia Publishing.

The wave-swept lighthouse is built on a rock pile or caisson. A local example is New London Ledge Light, the Second Empire-style lighthouse visible from the Gold Star Bridge.

“It's one of my favorites architecturally,” said D'Entremont, who notes in his book that its elaborate design was intended to appease the wealthy residents of the city's shoreline.

Built in 1909, Ledge Light survived the Hurricane of 1938 — as did the keeper in residence, Howard B. Beebe, who recounted later how waves flooded the building's second story.

Not all wave-swept lighthouses are located so close to shore. Their remote sitings and exposure to the elements made service in one of these lights the most challenging in the U.S. Lighthouse Service.

Imagine the terror of assistant keepers Joseph Wilson and Joseph Antoine at Minot's Ledge off Cohasset, Mass., the country's first “wave-swept” light.

In a furious April storm in 1851, just a year after the structure was built, the lighthouse began to sway. The two dropped a note in a bottle: “The light house won't stand over to night — she shakes 2 feet each way now.”

When the note was found by a Gloucester fisherman, both the lighthouse and its occupants had been washed away.

It was no wonder, if you consider its construction. It was perched 70 feet high on piles drilled into rock, and looked more like a water tower than a lighthouse. It became obvious to its early keepers that the iron lighthouse was vulnerable to both wind and waves.

After its loss, the U.S. Lighthouse Board designed a much sturdier granite light, which still stands today.

Minot's is another of D'Entremont's favorite lighthouses, although he concedes that singling one out is “like naming a favorite child or grandchild.”

“You wouldn't call it pretty,” he said. “It's striking.”

The book focuses as much on people as it does on architecture and engineering. D'Entremont says he sometimes gets choked up researching or lecturing about the fate of lightkeepers. “Walter Eberle was one of those stories.”

Eberle was the assistant lightkeeper on duty at Whale Rock Light off Narragansett Pier, Rhode Island, during the Hurricane of 1938. He did not fare as well as Howard Beebe of Ledge Light.

A “spark-plug” type lighthouse, Whale Rock was not affixed to a caisson but “was perched on rock,” D'Entremont said. “It was bolted to the ledge, and apparently not that well.”

Eberle was alone at Whale Rock on Sept. 21, 1938, when the wind and water began to rise. At some point in the screaming gale, the lighthouse toppled off its base and into the ocean.

Eberle's body was never found. He left behind a wife and six children.

D'Entremont tells harrowing stories of people driven to attempt murder or suicide by the isolation and demands of lightkeeping.

At Greens Ledge Light in Norwalk, in 1910, the lightkeeper stole away, leaving his assistant stranded without a boat for 11 days. A lighthouse tender found the assistant “nearly starved to death,” D'Entremont writes.

In New Haven, in 1907, the keeper of Outer Breakwall Light drowned while trying to reach shore in a small rowboat.

When not facing life-threatening storms, most lightkeepers found their biggest challenge was boredom.

They relied on books (and, later, TV) to while away the hours. In 1975, a lightkeeper at Halfway Rock in Casco Bay, Maine, told the Portland Press Herald a basketball had washed up and he had spent all day counting “2,448 pimples” on its surface.

Today the Coast Guard has automated its active lighthouses, mostly with solar-powered LED lamps, and some decommissioned lights have been restored by nonprofits or philanthropic individuals.

They remain a subject of endless fascination. D'Entremont makes his living by writing and lecturing about the subject, and gives tours each summer of Portland Head Light in Cape Elizabeth, Maine.

A New Hampshire resident, he is president of the American Lighthouse Foundation. For this book, he did extensive research through the National Archives, the U.S. Lighthouse Society, and the U.S. Coast Guard Historian's Office in Washington, D.C.

For all their beauty, D'Entremont has no romantic illusions about living on a wave-swept light.

“No, not at all. I know too much. I know what the life was like,” he said. “It was a hard job. Some places were harder than others.”