In spring 1942, the nation and its military leaders faced a dire disaster worse than Pearl Harbor.
German U-boats operating within the nation’s territorial waters were sinking Allied merchant vessels at an ever-increasing number and killing an appalling number of helpless noncombatants — more than 5,000 in fewer than six months, including some women and children. The largest concentration of losses to U-boat attacks occurred off the coast of North Carolina. Cape Hatteras was ground zero.
A late-March conference of naval officers formulating plans to implement protective convoys in U.S. waters determined that it would require 31 destroyers and 47 smaller patrol craft. On the day that their report was submitted to Adm. Ernest J. King, commander-in-chief of the U.S. Navy, there were but three destroyers on duty in the Eastern Sea Frontier and only eight other patrol craft.
Meanwhile, at any given time, there were as many as 140 unescorted ships headed northward between the Florida Keys and New York; an equal number of vessels were, at the same time, headed in the opposite direction. It has been estimated that, each day, there were 60 or more ships making their way north or south in the waters immediately off the North Carolina coast.
The protection of so many merchant ships from the onslaughts of what seemed to be phantom German U-boats was a daunting and nearly impossible task. But the inability of each ship’s cargo to reach its destination safely directly impacted the planning and preparations for an Allied invasion of Europe. A solution was imperative.
Lacking a sufficient number of warships to establish large coastal convoys in the first five months of the U-boat peril, naval authorities attempted to shuttle small groups of merchant ships up the coast during daylight in an operation called “Bucket Brigades.” Northbound ships were ordered to stop for the night at anchorages at Jacksonville, Florida, Charleston, South Carolina, the west side of Cape Fear, and the west side of Cape Lookout.
From Cape Lookout, tankers and freighters raced across the deadly 225-mile U-boat gauntlet in the Graveyard of the Atlantic before arriving at the entrance to Chesapeake Bay. Slower merchant ships unable to keep up with the Bucket Brigades were to stop for the night in an artificial offshore harbor established on the southwest side of Cape Hatteras and Diamond Shoals, encircled by a mined anchorage much like the British minefield guarding the Thames estuary.
On the western perimeter of the minefield, a few miles southeast of Ocracoke village, an opening wide enough for tankers to pass in and out of the protected anchorage led to a designated 36-square-mile box directly south and east of Hatteras Inlet where the ships were to drop anchor for the night.
Seventeen days after the Cape Hatteras protected anchorage opened for business, the Standard Oil tanker F.W. Abrams lost contact with its pilot boat while departing in poor visibility and struck a mine. The ship’s captain thought that they had been torpedoed. The anchor was lowered but the ship began to drift in the heavy rain and fog. In less than an hour, two more explosions rocked the ship, finally sinking it.
During World War I and after, Great Britain devised, tested and installed numerous technologies for anti-submarine detection at many of its strategic ports, harbors and outlying anchorages. One of the more intriguing and highly secret British technologies proved its effectiveness in 1918 — an underwater magnetic indicator loop.
Even when a U-boat’s magnetic field was degaussed, the steel hull continued to emit a small electric current that could be detected by electromagnetic induction via an underwater stationary loop of cable connected to sensing equipment on shore. By such a method in 1918 the British Navy detected the incursion of a German U-boat, UB-116, into the mined anchorage of the naval base at Scapa Flow in the Orkney Islands.
In support of the Cape Hatteras minefield, the U.S. Navy established in the summer of 1942 a magnetic indicator loop station on Ocracoke Island. The Navy chose a site atop an ancient sand ridge, about halfway between the village and the beach.
The ridge, 30 feet above sea level in places, overlooked a vast and barren tidal flat that separated the island’s beach and the village, but which has long since been covered by dunes and vegetation. The sand ridge provided a relatively high vantage point for the buildings and towers that would be built there; the setting also made the secret station plainly visible to the nearby island residents who were prohibited from venturing beyond the limits of the village during most of the war.
“They wouldn’t let nobody but a special certain people go into the enclosure out there,” former World War II Coastguardsman Ulysses “Mac” Womac told me in an interview in 2000. Womac was assigned to overnight beach patrols and often passed the station. “They had guards out to where nobody could get up to where they was at. They stood watch out there on the hill. In fact, they lived out there, a few of them did. And they stood watches and listened on earphones for what was offshore. Now, where they had the cable offshore I don’t know. But we saw it on the beach, or I did before they buried it.”
At other U.S. Navy indicator loop installations, the average length of a single loop field was 2 to 3 miles; the longest could be up to 6 miles long . The cables forming the two loops were spliced to a tail cable, which connected the array to the receiving station on shore. Tail cables could be many miles long depending on the distance from the receiving station to the location of the indicator loops offshore.
At Ocracoke’s loop receiving station, a concrete casemate housed the operations building that contained all the facility’s detection equipment including fluxmeters, chart recorders, communications gear, telescopes and furniture for four men. The Ocracoke station also was equipped with an early version of a microwave surface-search radar system, which was erected on top of the operations building.
Other cutting-edge detection technology included radio sonobuoys and high-frequency radio direction finding, also known as HF/DF or “Huff-Duff.” In addition to the “Huff-Duff” hut at Ocracoke’s loop receiving station, similar HF/DF receiving stations were located at Coast Guard Lifeboat Stations at Cape Lookout and Poyners Hill, which was south of the Currituck Beach Lighthouse.
When the Navy finally got done building, equipping and manning Ocracoke’s top-secret loop receiving station, it was one of the more complex, state-of-the-art defensive installations on the East Coast. But by the time the installation was operational, there were few, if any, U-boats operating off North Carolina’s coast for the station to detect.
The tide turned in the war zone in the western Atlantic when the first, fully escorted coastal convoys began transiting the middle-Atlantic states in mid-May. By then, the skies were patrolled by military and Civil Air Patrol aircraft. Small patrol vessels armed with two-way radios crisscrossed the sea lanes. Shorter periods of darkness also limited the time that German U-boat could safely recharge their batteries on the surface.
Between April and July, four U-boats were sunk by Navy and Coast Guard warships and an Army A-29 bomber off the Outer Banks. Germany began redeploying its U-boats to the North Atlantic and Mediterranean theaters in mid-July 1942. For the remainder of the year, 160 coastal convoys were conducted between Galveston and New York. During that time, only three Allied merchant vessels were sunk, and one was damaged by U-boats while the ships were shepherded in convoy.
A year after it was established, the Cape Hatteras minefield was swept by the Navy to remove the Mark-6 mines. Fewer than half of the mines moored in 1942 were recovered. Overall, it has been estimated that the U.S. Navy placed 20,000 mines in United States waters for defensive purposes during the war. Not a single German U-boat or Axis vessel was ever sunk by the mines, but three Allied vessels were destroyed by the Cape Hatteras minefield. And even to this day, a few of the rusty, barnacle encrusted contact mines wash up on a North Carolina beach.