"The Listeners: U-boat Hunters During the Great War"

By Roy R. Manstan

Wesleyan University Press, 336 pages

Groton is known as the Submarine Capital of the World, but New London could once lay claim to the opposite title: Anti-Submarine Capital. 

During the Cold War, Fort Trumbull was home to a research site known variously as the Navy Underwater Sound Laboratory, Naval Underwater Systems Center and Naval Undersea Warfare Center. The lab grew out of World War II research there aimed at countering the Nazi submarine threat.

Less well-known is that the fort was also a major anti-submarine center during World War I, when America’s undersea fleet was in its infancy and German U-boats ruled the high seas.

A new book by a veteran Sound Lab engineer chronicles the Allies' desperate effort to defeat the U-boats; the prominent role played by scientists in New London is central to the story.

"The Listeners: U-boat Hunters During the Great War" takes in the full sweep of submarines' crucial role in the conflict, from the sinking of the Lusitania to the unrestricted submarine warfare that dragged the U.S. into the fight. But the focus is on British, French and especially American scientists' efforts to confront a new challenge in warfare: how to defeat an unseen enemy.

At the time, the modern submarine was new, untested and dismissed as nothing more than a harbor patrol craft. That attitude changed in a hurry once U-boats started systematically sending Allied ships to the bottom.

With the land war stalemated in the trenches of the Western Front, U-boats threatened to tip the balance if they could sink enough merchant ships to starve England into submission. How to stop them?

As author Roy R. Manstan explains, if invisibility was U-boats' armor, engines and propellers were their Achilles' heel: They could be heard.

This fact formed the basis for most efforts to counter the U-boat threat. The invention of increasingly sophisticated underwater listening devices led to the ability to home in on their location and, ideally, deliver a death blow.

As the United States prepared to enter the war in early 1917, government and military officials realized combat with U-boats was not far off, and the nation lacked any practical know-how.

When the bureaucracy geared up to seek solutions, several divides emerged among those involved that threatened overall cooperation: the Navy vs. civilians, academia vs. industry and, most important, scientists vs. engineers.

This last one was fueled by the attitude of Thomas Edison, who helped organize the effort. When scientists were found to be underrepresented on committees, an associate explained that the great inventor wanted "practical men who are accustomed to doing things, and not talking about it."

The Navy established an experimental station at Nahant, Mass., but when the engineering ethic prevailed there, a need was seen for a second site where scientists, guided by physics, could conduct extensive testing.

Under the leadership of physicist Robert Millikan, who was a few years away from winning a Nobel Prize, the nation's best scientific minds came together at a logical place: across the river from where the nation's first submarine base had just been established.

By the fall of 1917, with the Nahant and New London stations both up and running, engineers and scientists were reviewing mostly poor anti-submarine technologies developed by their British and French counterparts and trying to come up with something better.

A dizzying array of listening devices, or "hydrophones," were invented and tested. The idea was to lower them into the water, usually from a ship, listen for a distinctive U-boat sound, pinpoint its direction and distance, then drop depth charges.

Keeping track of all the devices described and their alphabet-soup names (C-tube, K-tube, etc.) is daunting, but the author is good about not losing the general reader in technical details. What's striking is the sheer number of inventions, which speaks to the scientists' make-it-up-as-you-go determination to find something that worked in time to change the course of the war.

Recognizing the right sounds, through stethoscope-like earpieces, was a specialty that involved training in New London. Those who acquired the skill (the "listeners" of the book's title) were then assigned to various vessels that hunted U-boats.

Submarines, destroyers, converted yachts and even seaplanes were tested for this task, and all became a common sight at Fort Trumbull. But the ideal U-boat hunter turned out to be a humble, 110-foot wooden craft called a submarine chaser, which had the speed and maneuverability to outrun U-boats once they were heard.

More than 400 were quickly hammered together at shipyards around the country and funneled through New London, where listening devices were installed and the 24-man crews trained. More than 100 then set out for Europe in three-stage convoys: New London to Bermuda to the Azores to Gibraltar.

The New London experimental station, shrouded in secrecy, faced several obstacles, including the epic winter of 1918, which froze much of the Thames River, and the presence of German spies. An entertaining first-person account of a Navy man's encounter with a spy is quoted at length, one of many period voices that bring the story to life.

The book, a slightly oversize hardcover, is compellingly readable and lavishly illustrated, often with the constantly evolving hydrophones, photos of which were preserved in a family archive.

Manstan organizes the story well, though the narrative moves at different speeds: briskly when covering the big picture or human interactions, and more slowly, though always clearly, when describing devices and the science behind them. Every chapter begins, effectively, with a quote from a report, speech or memoir from the time.

As the scientists proceeded with their work, the cat-and-mouse game of technological advances played out on both sides. Equipped with devices of their own, U-boats listened to the listeners and foiled them by resting silently on the bottom. One response to this was a weighted wire that sub chasers dragged across the sea floor. When it made contact with a U-boat, a buzzer alerted the crew.

The war's unexpected end in November 1918 left the story of the U.S. anti-submarine effort unfinished. Just a handful of U-boats were destroyed thanks to listening devices, but the game had changed. Submarines had once operated with impunity; now they were constantly on guard, their tactics reflecting the new reality.

The primitive but ingenious devices developed by scientists in New London gave way to a more promising technology that matured too late to factor in the war: echolocation, or the use of sound waves to locate an object. This was the future of submarine detection and of another half-century of research in New London.

The details of those later days are better-known, and the Sound Lab’s World War I origin story has long needed to be told. "The Listeners" fills that void ably for both local interest and broader military history.

j.ruddy@theday.com