The “CHEAP” British Frigates That Killed More U-Boats Than Destroyers

July 31st, 1944.

The Western approaches 60 mi southwest of the Silly Isles.

HMS L Kllin, a frigot displacing 1,435 tons, is hunting a submarine.

She has been in commission for barely 3 months.

Her hull was welded together from pre-fabricated sections in a civilian shipyard that had never built a warship before the war.

Her crew of 114 includes reserveists who had never seen the open ocean before 1939.

On her for deck sits a weapon that has never been fired in anger against a real target.

The sonar operator reports contact range 800 yd bearing steady.

The target is U333, a veteran type 7 seabo on her 12th combat patrol.

She has sunk seven merchant ships totaling 32,17 gross register tons.

Her crew have survived 3 years in the North Atlantic.

They know every trick an escort vessel can throw at them.

They have evaded depth charges, outrun corvettes, and dived beneath destroyer attacks that would have killed lesser boats.

Lieutenant Commander Stanley Darling, Royal Australian Naval Volunteer Reserve, orders the new weapon loaded, three barrels, three full-size depth charges, each weighing 390 lb, packed with 27 lb of manol explosive.

The type 147B depth finding sonar locks the target’s depth and feeds it directly to the weapon’s clockwork fuses.

The range closes at 2 75 yds.

The sonar range recorder triggers the weapon automatically.

No human decision in the final moments.

Pure mathematics.

Three charges arc forward in a triangular pattern.

They detonate above and below U333 simultaneously, creating converging shock waves designed to crush a submarine’s pressure hull from two directions at once.

45 men die instantly.

No survivors.

No debris worth recovering.

The entire attack from detection to kill takes minutes.

That weapon was called the Squid.

That frigot was a lock class, one of 28 built.

And that kill was the first confirmed submarine destruction by the most lethal anti-ubmarine weapon of the Second World War.

The Squid achieved a kill rate of 40.7% per attack.

Standard depth charges managed 1.65%.

The frigots that carried the squid cost a fraction of a fleet destroyer and were assembled in yards that had spent the peaceime years building trwers and coastal freighters.

How did a class of cheap mass-roduced escorts dismissed as tin cans by skeptics in the Admiral Ty become the deadliest submarine killers in the Royal Navy? The answer begins with a crisis that nearly lost the war before a single Allied soldier set foot in France.

By the spring of 1942, Britain was being strangled.

Yubot sank 868 Allied ships in the first 8 months of that year, totaling 3.1 million tons of cargo sent to the bottom.

German submariners called it the second happy time.

In June alone, losses reached 637,000 tons.

Britain could replace only 1.25 million tons of shipping per year.

The mathematics were terminal.

At that rate, the island nation would run out of fuel, food, and ammunition before the end of 1943.

An oil deficit of 2 million tons was forecast for the coming winter.

Winston Churchill, a man who had faced the fall of France, the Blitz, and the Japanese conquest of Singapore without flinching, wrote after the war that the yubot peril was the only thing that truly frightened him during the entire conflict.

He was right to be afraid.

The Royal Navy had started the war with 146 destroyers.

By 1941, half were sunk or crippled.

Fleet destroyers were the obvious answer to the submarine threat.

fast, well-armed, capable of hunting and killing any yubot afloat.

They were also phenomenally expensive.

A tribalclass fleet destroyer cost approximately 520,000, took 18 to 24 months to build in a specialist naval dockyard, and required turbine engines that only a handful of manufacturers in Britain could produce.

The Admiral T could not spare them from screening the home fleet, escorting capital ships, and supporting offensive operations in the Mediterranean.

The 50 obsolete American forest stackers received through the destroyers for bases agreement were stop gaps at best, worn out, mechanically unreliable and loathed by the crews who sailed them.

That left the flowerass corvettes, 294 were built, and by 1942 they made up half of all allied escort vessels.

The corvettes were heroic ships.

They saved thousands of lives.

They were also fatally limited for the role they were asked to perform.

Maximum speed 16 knots.

A surface type 7 CU boat made 17.7.

The corvettes could not catch the enemy they were supposed to kill.

Endurance was 3,500 nautical miles at 12 knots.

Not enough to cross the Atlantic without refueling.

They displaced barely a thousand tons.

In North Atlantic winter storms, they rolled 80°.

Their single screw and short waterline made them sluggish in turns, exactly when rapid maneuvering was essential for depth charge attacks.

Accommodation was so wretched that crews called them floating prisons.

Churchill himself described them as cheap and nasty.

Compounding every problem was the Mid-Atlantic Gap, the area roughly 300 m wide where no land-based patrol aircraft could reach.

The crews called it the Black Pit.

In that void, wolf packs of 10, 15, 20 yubot attacked convoys for days without interference from the air.

Escorts fought alone, outnumbered, outpaced, and exhausted.

The crisis peaked in March 1943.

In the first 20 days of that month, sank 120 ships totaling 693,000 tons.

Only 12 Ubot were destroyed in return.

The historian Steven Roscll wrote that the Germans never came so near to disrupting communications between the new world and the old.

As in those 20 days, Britain had roughly 12 weeks of oil reserves remaining.

If the convoy stopped, the war was over.

The Admiral T needed a new type of warship, faster than a corvette, cheaper than a destroyer, simple enough for civilian yards to build in numbers, lethal enough to hunt rather than merely endure their attacks.

and it needed them not in years but in months.

The man who delivered the solution was William Reed, a naval engineer at Smith’s Dock Company in South Bank on Tees Middlesborough.

The same firm that had designed the flower class corvette Hull.

Reed received his brief from the Admiral T in late 1940.

create a warship that combined the endurance and anti-ubmarine capability of the expensive Black Swan class sloops with the cheap rapid construction methods of the Corvettes.

His solution was elegant in its simplicity.

He doubled the Corvette’s machinery.

Two four-cylinder vertical triple expansion steam engines producing 5,500 indicated horsepower on two shafts fed by two Admiral Ty three drum water tube boilers.

One historian described it as simply the flowers machinery doubled, drawing steam from more efficient boilers.

The deliberate choice of reciprocating engines over turbines was the pivotal decision.

Triple expansion engines could be manufactured by any competent civilian engineering works in approximately 16 weeks.

Turbines took 7 months or more and required specialist facilities that were already working at full capacity on fleet destroyer orders.

The engines were also instantly familiar to the reserveist and volunteer crews who would man the ships.

These were men from the Merchant Marine, Royal Naval Reserve, and Royal Naval Volunteer Reserve ratings who had worked with reciprocating steam their entire careers.

The hall was built to mercantile construction standards, not full warship specifications.

A flat transom stern, simplified fabrication, and improved hydrodnamics.

A raised for castle extending well aft transformed seaeping compared to the corvettes.

The result was the riverclass frigot.

The word frigot itself, absent from the Royal Navy since the age of sale, was revived in 1942 at the suggestion of Vice Admiral Percy Nells of the Royal Canadian Navy, replacing the awkward original designation twin screw corvette, 1,445 tons standard displacement, 2,110 tons at deep load, 301 ft 6 in in length overall.

Beam 36 ft 6 in.

Draft approximately 12 ft.

Maximum speed 20 knots.

Fast enough to catch a surfaced yubot and return to the convoy after breaking off pursuit.

Range 7,200 nautical miles at 12 knots.

Nearly double the flower class.

Standard armament comprised two QF4 in Mark19 guns on a twin high angle low angle mount forward.

One hedgehog 24 spigot mortar up to 150 depth charges deployed from rails and four throwers.

Eight 20 millimeter orlicon anti-aircraft guns in single and twin mounts.

Sensors included type 144 ADIC sonar for submarine detection.

type 271 or 272 surface search radar for detecting surface Ubot at night and HFDF direction finding equipment known as Huffduff for intercepting and triangulating Ubot radio transmissions.

Crew complement was 140 to 157 officers and ratings.

151 riverclass frigots were launched between 1941 and 1944 for seven allied navies.

Britain, Canada, Australia, France, the Netherlands, the United States, and South Africa.

Construction was spread across dozens of civilian yards.

Smith’s Dock, Henry Rob and Leath, Charles Hill, and Sons in Bristol, Blith Drydock, and Harland and Wolf in Belfast among the British builders.

Canadian production centered on Yeros Limited in Eskimalt and Canadian Vickers in Montreal.

The Riverclass proved the concept.

The Admiral T wanted the next step.

The lock class designed from late 1942 was not merely an improved frigot.

It was a warship designed from the keel up around a single weapon, the squid mortar.

Two triple-barreled squid launchers sat on the shelter deck behind protective bull works, replacing the exposed hedgehog position that had drenched crews with North Atlantic spray.

A single 4-in gun was mounted forward on the main deck.

Because the Squid was so effective that prolonged depth charge battles became unnecessary.

Depth charge storage was slashed from 150 to just 15.

The Hull introduced pre-fabricated modular construction.

Sections were limited to 29 ftx 8t 6 in x 8’6 in sized to fit standard railway flat cars and light cranes.

13 shipyards built whole sections.

Five acted as specialist outfitters.

Six supplied complete bridges and superructures.

28 Lockclass frigots were completed entering service from April 1944.

Displacement 1,435 tons standard 2,260 deep load.

Length 307 ft.

Beam 38t 6 in.

Speed 19.5 to 20 knots.

Range 9,500 nautical miles at 12 knots.

Crew 114.

Fewer men than the riverclass in a larger, more lethal ship.

The weapons that these frigots carried demand explanation because they change the mathematics of submarine warfare entirely.

The fundamental problem with depth charges was geometry.

To attack, the escort ship had to pass directly over the submarine before dropping charges as stern.

In the final 200 yards of the approach, Azdic contact was lost as the sonar beam passed over the target.

The Ubot could hear the escort’s propellers, estimate the moment of attack, and maneuver to evade.

The standard Mark 7 depth charge weighed 420 lb, sank at 7 to 10 ft per second, and had a lethal blast radius of only 20 ft.

Explosions created air bubbles that temporarily blinded sonar, preventing immediate reattack.

The result was devastating for the attackers, not the attacked.

Depth charges achieved kills in 1.65% of attacks.

85 12 kills from 5,174 attacks across the entire war.

The Hedgehog changed the equation.

Developed by the Admiral T’s Directorate of Miscellaneous Weapons Development, it fired 24 contactfused projectiles in a circular pattern 250 to 300 yards ahead of the ship.

The Escort maintained sonar contact throughout the attack.

If every projectile missed, they sank silently.

No explosions, no sonar disruption.

Immediate reattack was possible.

Kill rate 17.5%.

47 kills from 2 68 attacks.

No submarine is known to have survived a single hedgehog hit.

The Squid was the revolution.

Three full-size depth charges fired in a triangular pattern 275 yd ahead.

Unlike the Hedgehog’s contact fuses, Squid used clockwork time fuses automatically set by the Type 147B depth finding sonar.

The depth setting updated continuously until the instant of firing.

The weapon was triggered automatically by the sonar range recorder.

A double squid installation standard on lock class frigots fired six charges in two opposing triangles set to detonate 25 ft above and below the target, creating converging pressure waves.

Kill rate 40.7%.

11 kills from 27 attacks, nine times more effective than depth charges.

Twice as deadly as the hedgehog.

The frigots carried these weapons into combat and the results were extraordinary.

HMS Spay, a riverclass frigot, accounted for three confirmed Ubot kills.

On February 18th, 1944, while screening convoy224, Spay detected U406 on sonar.

A sustained depth charge attack forced the submarine to the surface.

Spay’s gun crew destroyed her with direct fire.

The following day, February 19th, SPY located and sank U386.

Two Ubot eliminated in 24 hours by a single frigot, displacing less than half the tonnage of a fleet destroyer.

HMCS Waskeu, a Canadianbuilt riverclass, engaged U257 on February 24th, 1944.

The frigot’s depth charges drove the yubot to the surface.

Waskeu’s gun crew scored four hits on the conning tower with the main 4-in armament.

The submarine sank with all visible crew on deck in the war’s final weeks.

HMCS La Huluas Strathadam and Thatford mines combined to destroy U1302 in St.

George’s Channel on March 7th, 1945.

The Lock class took the killing to another level.

returned to HMS L Killllan after her first squid kill on July 31st.

She was hunting again 6 days later.

August 6th, 1944, the Bay of Bisque.

U736 fired a torpedo directly at Lach Killllin.

A port lookout spotted the periscope.

Darling ordered the squid fired.

The detonation did something nobody had anticipated.

The shockwave countermined the incoming torpedo, neutralizing it before it reached the ship.

The blast then forced U736 to the surface directly beneath the frigot’s stern.

The two vessels collided and locked together.

German crewmen scrambled up onto Lock Killllan’s quarter deck.

For several minutes, the crews of Hunter and Hunted stood face to face on the same deck, staring at each other in mutual astonishment.

Then U736 slipped free and sank.

28 killed, 19 survivors pulled from the water.

On April 15th to 16th, 1945, off start point in Devon, Lach Killllin detected U 1063.

Three squid salvos forced the submarine to the surface with a jammed rudder.

17 survivors rescued, three confirmed kills, all by squid.

Lieutenant Commander Darling received a second bar to his distinguished service cross.

HMS Lock Dunvigan participated in the destruction of U354 during Arctic convoy JW59 on August 24th, 1944 in the Barren Sea.

HMS Lock inch destroyed U307 on April 29th, 1945, using squid to force the boat to the surface before gunfire from four ships finished her in 8 minutes.

Not a single lockass frigot was lost to enemy action during the entire war.

The broader picture reinforces the point.

The arrival of riverclass frigots in significant numbers coincided with the turning point of the Atlantic War.

In May 1943, the month the Allies called Black May, 41 Yubot were destroyed.

That was 25% of Germany’s operational submarine strength gone in 30 days.

Donuts ordered a general withdrawal from the North Atlantic on May 24th, admitting that losses were caused by the superiority of enemy location instruments.

The riverclass and captainclass frigots form the backbone of the new roving support groups that made this slaughter possible.

Freed from close escort duty, these groups hunted yubot to destruction across hundreds of miles of open ocean.

Captain Frederick John Walker, the war’s most successful anti-ubmarine commander, demonstrated what aggressive frigot type escorts could achieve.

His second support group operating from Gladston dock and Ball destroyed six Yubot in 27 days during January and February 1944 expending 634 depth charges.

On February 9th alone, the group sank three submarines U734, U238, and U762.

Walker drove his crews relentlessly.

When his depth charge magazines ran dry, he had them replenished from passing merchantmen and continued the hunt.

He was credited with 20 yubot kills under his direct command before dying of cerebral thrombosis from exhaustion on July 9th, 1944, aged 48.

His funeral procession through Liverpool drew thousands of mourners.

The tactics he pioneered, the creeping attack and coordinated multi-ship prosecution, became standard doctrine aboard every frigot in the fleet.

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The real measure of the British frigot is direct comparison against the ships it replaced, against the fleet destroyers it supplemented, and against the American equivalent designed for the same mission.

A flowerclass corvette displaced 1,000 tons, made 16 knots, carried up to 70 depth charges, had a range of 3,500 nautical miles, and crewed 85 men.

A Riverclass frigot displaced 1,445 tons, made 20 knots, carried a hedgehog plus 150 depth charges, ranged 7,200 nautical miles, and crewed 157.

The frigot was four knots faster, double the range, and carried a weapon 10 times more lethal.

A tribal class fleet destroyer displaced 1,854 tons, made 36 knots, and cost approximately 520,000.

A Riverclass frigot cost roughly half that figure.

The destroyer required a specialist naval dockyard and turbines that took 7 months to manufacture.

The frigot was built in a civilian yard using engines produced in 16 weeks.

For every fleet destroyer the Admiral T ordered, it could put two frigots to sea in less time, both carrying superior anti-ubmarine weapons.

The American comparison deserves fairness.

The United States produced 154 Buckley class destroyer escorts, 78 of which served in the Royal Navy as captainclass frigots.

American industrial capacity was extraordinary.

HMS Holstead was built in 24 and a2 days.

American destroyer escorts were faster at 24 knots and carried heavier gun armament.

They were excellent ships, but the Americans were fighting a different war across different distances.

Their destroyer escorts operated with carrier groups in the Pacific and on Atlantic routes with shorter transits and better air cover.

The British Frigot was designed for the North Atlantic at its worst.

Weeks at sea in mountainous swells.

No air support.

Hunting submarines with three years of experience.

The riverclass and lock class were optimized for that specific hell.

And the squid equipped lock class had no American equivalent.

No other navy deployed a weapon system with a 40% kill rate per attack.

The German Naval War Diary for July 1943 acknowledged that the invisibility of the Yubot was gone.

Grand Admiral Dunitz testifying at Nuremberg in May 1946, identified Allied radar and aircraft as the war-winning combination.

Herbert Werner, a Yubot officer who survived three boats and the 75% casualty rate among German submariners, wrote in his memoir, Iron Coffins of Patrols, in 1944, where entire groups deployed and only one boat came home.

Approximately 30,000 of the 40,000 men who served in Yubot were killed.

The ocean they had once dominated became their cemetery.

Think back to that moment.

July 1944, the Western approaches.

HMS Lock Killllin, three months in commission.

114 men, most of them reserveists.

A hull welded together from prefabricated steel sections in a shipyard that had built trwers before the war.

A weapon system that had never been tested against a real submarine against her U333.

12 patrols completed, seven ships destroyed.

A crew forged by three years of combat in the deadliest theater on Earth.

The frigot killed the submarine with a single salvo, then destroyed another six days later, then sent a third to the bottom 8 months after that.

The admirals who said convoy escorts needed fleet destroyer speed were wrong.

The accountants who said cheap ships could not match expensive ones were wrong.

The marina submariners who believed they could outmaneuver any escort were wrong.

151 riverclass, 28 lock class, 78 captain class.

Built in civilian yards by workers who had never touched a warship, crewed by volunteers who had never crossed an ocean, armed with a weapon that killed submarines 40% of the time it was fired.

1.65% 65% with depth charges, 40.7% with the Squid, a 24-fold increase in lethality carried aboard ships that cost half as much as a destroyer and could be built in half the time.

Tin cans.

That is what the skeptics called them.

The 250 Ubot sent to the bottom by surface.