It was July 21, 1918 and World War I was in its final year.

The Perth Amboy, a tugboat owned by the Lehigh Coal & Navigation Co., and four barges were traveling off the coast of Cape Cod when a German submarine surfaced.

The U-boat attacked the unarmed tugboat and barges. Shells fired by U-156 landed on the shores of the tiny seaside town of Orleans, Mass., making it the only U.S. land to be struck by enemy fire during the war.

This little-known event is the subject of a new book, Jake Klim's "Attack on Orleans: The World War I Submarine Raid on Cape Cod" (History Press, $19.99, 128 pp).

Central to the book is the tugboat owned by Lehigh Coal & Navigation.

The company, based in Mauch Chunk (now Jim Thorpe), provided water supplies and shipping services in the Lehigh Valley region. It's also known for its construction of the Lehigh Canal.

"The Attack on Orleans" is a detailed historical account, but also has a breezy, journalistic style that can be appreciated by casual history lovers.

Klim, a documentary TV producer in Washington, D.C., developed an interest in the battle as a kid growing up just 20 miles from Orleans.

"I tell stories for a living and I'm a history geek," Klim says. "I happened to start digging in it one day and the more I dug into the history I learned there's also a lot of folklore."

Klim sets the stage for the attack, telling first the story of the USS San Diego, which was en route to New York when an explosion ripped through the hull.

"It had taken only 28 minutes for the San Diego to sink," Klim writes.

There were no signs of a submarine, so much debate ensued about what sank the ship.

Despite what happened to the San Diego, crew members aboard the Perth Amboy and its vessels weren't concerned. They believed they were safe because they were so close to shore.

"'The Perth Amboy was the finest tug in the fleet,' boasted the manager of the freight company, and although the Cape was notorious for bad weather, on July 21, 1918, the sea was eerily calm," Klim writes.

The barges pulled by the tugboat were largely empty. Only one of the four barges had any cargo.

The vessels were carrying 32 people; many were Portuguese who had just immigrated to America. Also on board were the four wives of the barge captains and five children.

"Just before 10:30 that morning," Klim writes, "a deckhand on the Perth Amboy was startled by the sight of something white skipping through the water."

The German sub attacked the ships with torpedoes and then shells. The blast of a shell crashed through the tug's pilothouse, injuring John Bogovich, who was at the helm of the tugboat.

"Stunned and shaken, he noticed that his right arm was nearly severed with two deep, jagged wounds above his elbow," Klim writes.

Later, the tugboat's Capt. James Tapley would write a letter to family members about the attack, according to genealogy website PA-Roots: