HMS Thornborough (K574): An American-Built Frigate Fighting E-Boats off Normandy

Built in Massachusetts, Promised to Britain

HMS Thornborough was built by the Bethlehem Steel Company at Hingham, Massachusetts, laid down on 22 September 1943 and launched that November.

Remarkably, she had already been assigned to the Royal Navy under the Lend-Lease agreement back in June, before her construction even began, and she commissioned into British service on 31 December 1943, a Captain-class frigate built in America specifically to help make good Britain's shortage of escort vessels.

The arrangement that produced her is worth a note. Britain needed escorts faster than British yards could build them, and the United States had shipyards that could turn out a destroyer escort in weeks; seventy-eight of them were handed over under Lend-Lease and became the Captain class, named after Royal Navy captains of the Nelson era. Being assigned to the Royal Navy in June 1943, three months before her keel was laid, was normal rather than remarkable: these ships were allocated off a production schedule. Several of her sisters from the same Hingham yard are here, including HMS Holmes (K581) and HMS Riou (K557).

Screening the Channel for D-Day

Thornborough spent 1944 operating extensively in European waters, serving in the English Channel and off Normandy as a radar escort for motor torpedo boat groups, providing the crucial early warning and coordination that allowed Britain's fast attack craft to operate effectively against German shipping in the crowded, dangerous waters surrounding the invasion beaches.

The Frigate as a Pair of Eyes

Radar escort for motor torpedo boat groups is a job title that conceals one of the cleverest tactical developments of 1944, and it is worth setting out because it is what she actually did for a year. The problem was E-boats: fast, low, wooden-hulled German torpedo craft based at Le Havre and Boulogne, which came out at night into the invasion anchorage where thousands of ships lay at anchor and could not manoeuvre. British motor torpedo boats could match them for speed and firepower. What British motor torpedo boats could not do was find them, because a small boat's radar sits eight feet above the water and sees almost nothing.

The answer was to pair them. A frigate like Thornborough, with a proper radar set high up, a plotting table, an operations room and long-range radio, would take station offshore and simply watch: not to fight, but to hold the picture. When a contact appeared she vectored her own group of motor torpedo boats onto it by radio, gave them the course, the range and the closing rate, and sent them in. The small boats did the fighting in the dark at fifty yards; the frigate did the seeing from five miles away. It was called control, and the principle, one platform with the sensors directing several without them, is the ancestor of every air defence and surface warfare system afloat today.

It also meant a frigate spent night after night in the Channel doing something that produces almost no personal narrative: no boarding, no rescue, no dramatic gun action, simply a long dark watch in an operations room lit by a radar display, talking small boats onto other small boats. It was the least visible and one of the most effective things done in those waters in 1944.

Hunting E-Boats

Between July and August 1944, Thornborough engaged German E-boats off Cape d'Antifer and attacked a German convoy, adding directly to the pressure on German coastal forces attempting to interfere with the Allied build-up in Normandy.

That November, she took part in further action against enemy E-boats in the Scheldt Estuary, part of the ongoing effort to secure the vital approaches to Antwerp as Allied forces pushed into the Low Countries.

Her itinerary in 1944 traces the retreat of the German coastal forces exactly. In June they came from Cherbourg, and losses in the first week were so heavy that the survivors were pulled back to Le Havre; Cherbourg fell on 26 June and the fighting concentrated off Cape d'Antifer, on the approaches to Le Havre, which is where Thornborough was in July and August. Then the Allied armies took the Channel ports and the E-boats withdrew again, to the Dutch coast and the mouth of the Scheldt, which is where she was in November, because that is where the war had gone: the approaches to Antwerp, which had to be opened before the armies in Belgium could be supplied at all. What that involved is described in HMS Stevenstone.

Patrols Through to War's End

Thornborough continued North Sea and Atlantic patrol duties through the remainder of the war, steady, essential escort work that rarely made headlines but kept vital shipping lanes secure during the war's final, hard-fought months.

Returned to America, and Scrapped in Greece

With the war won, Thornborough was nominally returned to the United States on 30 January 1947, her name struck from the American naval register the following week. She was sold that April to the Athens Piraeus Electricity Company in Greece to be broken up, an unremarkable end for a frigate that had played a properly useful role protecting the Normandy invasion fleet.