Late 1943, somewhere in Britain, engineers gathered around what looked like a farming accident welded to a tank. Two massive steel arms jutted forward from a Sherman holding a spinning drum covered in heavy chains. When they switched it on, the chains whipped the ground like a medieval torture device gone berserk.
Dust exploded everywhere. The noise was deafening and buried test mines detonated harmlessly, one after another, beaten to death before they could kill anyone. The watching officers thought it looked insane. They were right. But this insane machine would clear the beaches on D-Day when nothing else could.
The problem was simple and terrifying. By 1944, German engineers had planted millions of mines across occupied Europe. Field Marshal RML, commanding Army Group B, personally directed the fortification of the Atlantic Wall and understood that the invasion would be decided on the beaches within the first 24 hours. His solution was density.
pack the landing zones with so many obstacles and mines that Allied armor could never get ashore in sufficient numbers to establish a beach head. The Telmine, Germany’s standard anti-tank weapon, packed 5 kg of TNT and could rip the belly out of any Allied tank. It required only 90 kg of pressure to detonate, meaning any vehicle heavier than a motorcycle would trigger it.
German minefields stretched hundreds of meters deep with mines buried just below the surface every few meters. and the beaches of Normandy, where the Allies plan to land, were seeded with thousands of them. RML pushed for tens of millions of mines along the entire Atlantic coast.
He received far fewer, but still enough to turn the beaches into a trap. Clearing mines by hand meant engineers crawling forward with bayonets. Probing the soil centimeter by cime while German machine guns swept the beach. At Lamagne in 1942, this approach produced casualty rates that made commanders sick. One British report noted that sappers were being killed faster than they could clear lanes for the armor to advance.
The mathematics were brutal. A trained engineer took approximately 2 minutes to locate and disarm a single mine. A minefield 500 m deep might contain 300 mines per lane. At 2 minutes each, clearing one lane took 10 hours, assuming the engineer survived that long. Nobody did. Mine rollers offered one alternative.
Heavy wheels pushed ahead of a tank would detonate mines by pressure. The Soviets developed the PT34 system using weighted axles that could withstand 8 to 10 explosions before needing replacement. But rollers had critical flaws. Mines could be pushed downward into soft soil rather than detonating. On slopes, effectiveness dropped dramatically, and the roller only covered the width of the tank tracks, not the full vehicle, leaving the belly vulnerable to mines between the tracks.
What the British needed was something that could clear a full lane width, work on any terrain, survive multiple mine strikes and move fast enough to keep pace with an assault. According to Royal Engineers assessments from 1943, no existing technology met even half these requirements. The solution came from South Africa. Captain Abraham Dutis of the South African Defense Force conceived an elegantly brutal idea in 1941.
Instead of trying to detect mines or roll over them, why not simply beat the ground until they exploded? He envisioned a spinning drum carrying heavy chains that would hammer the earth ahead of a tank, detonating any mine within reach. The crew would stay safely inside the armored hull while the chains took the blast.
Douit filed his British patent on March 24, 1942 and was sent to England to develop the concept with AEC Limited, a company better known for building London buses. The result was the Matilda Baron, the first working flail tank. Simultaneously, Captain Norman Bry developed a similar system in Egypt called the Scorpion, which saw combat at Lalamagne in October 1942.
Both designs shared a fatal weakness. They relied on external auxiliary engines mounted beside the hull to power the flail drum. This made the vehicles too wide for transport, created vulnerable targets for enemy fire, and complicated logistics with separate fuel and spare parts requirements. The auxiliary engines also overheated constantly in desert conditions and choked on the very dust the flails created.
The breakthrough came when engineers realized they could power the flail directly from the tank’s main engine through a power takeoff system. A drive shaft running down the right side of the hull through a reduction gearbox would spin the drum without any external engine. This eliminated the auxiliary power plant entirely, keeping the vehicle narrow enough for standard transport and removing the most vulnerable component.
The base vehicle chosen was the Sherman Mark 5, known to the Americans as the M4 A4. Britain received nearly the entire production run of this variant under lend lease, approximately 7,167 tanks. Because the United States Army designated the M404 primarily for export, the heart of this Sherman was the Chrysler 57 multi-bank engine, one of the strangest power plants ever fitted to a fighting vehicle.
30 cylinders arranged as five inline six banks in a star pattern, displacing 20.5 L and producing 425 horsepower. The engine weighed over 2,200 kg with accessories, but proved remarkably reliable, achieving 240 hours mean time between failures. This power was essential. The flail mechanism demanded enormous energy while the tank still needed to move and maneuver.
The completed Sherman crab weighed 32 tons, roughly two tons heavier than a standard Sherman due to the flail mechanism, blast shield, and associated equipment. The Hull machine gun was removed because the blast shield between flail and hull blocked its field of fire, reducing the crew from five men to four.
Armor protection remained standard Sherman values. The glacis plate measured 50 to 51 mm angled at 56°, providing roughly 90 mm of effective thickness against incoming fire. The turret front was 76 mm thick with 38 mm protecting the sides and rear. The flail drum carried 43 heavy chains, each ending in a fist-sized steel ball.
When spinning at 142 revolutions per minute, these chains hammered the earth with devastating force, detonating mines buried up to 5 in deep. A single crab cleared a path approximately 3 m wide. The standard formation deployed three crabs advancing an echelon, creating a combined lane roughly 20 m across with two additional tanks providing fire support and standing ready to replace any disabled flail.
Speed while flailing was limited to between 1 and a/4 and 2 mph, essentially walking pace. Faster movement meant the chains couldn’t strike the ground densely enough, leaving gaps where mines might survive. The driver navigated by compass because the spinning chains kicked up blinding clouds of dust and debris. Disc cutters mounted at both ends of the drum sliced through barbed wire, making the crab effective against multiple obstacle types simultaneously.
Now, before we see how this performed in combat, if you’re enjoying this deep dive into British engineering, hit subscribe. It costs nothing, takes a second, and helps the channel grow. Right back to the Crab. The Crab Mark II introduced a contouring system that automatically adjusted flail height based on terrain. A counterweighted jib naturally assumed the correct position through force balance against the spinning drum, ensuring mines in dips and hollows were not missed.
This solved a major problem from earlier designs where fixed height settings left dangerous gaps in uneven ground. One critical limitation shaped crab tactics. The main gun could not fire while flailing. The turret had to rotate rearward to protect the 75 mm gun tube from debris and blast damage. This left crabs temporarily defenseless during clearing operations.
Crews carried 97 rounds of ammunition and could engage targets normally when not flailing. But during mine clearing, they depended entirely on supporting tanks for protection. The project fell under Major General Percy Hobart’s 79th Armored Division, formed in August 1942. Hobart was a brilliant but difficult officer who’ commanded the Seventh Armored Division, the famous Desert Rats, before being forced into retirement in 1940.
Winston Churchill personally intervened twice to reinstate him, overriding military establishment resistance, the division’s distinctive Black Bull insignia became synonymous with the Specialized vehicles collectively known as Hobart’s Funnies. By March 29, 1944, the British Army had ordered 689 Sherman crabs for conversion with production estimates suggesting approximately 1,000 total units.
The 30th Armored Brigade comprising the Lotheians and Border Horse, 22nd Draons, and Westminster Draons would operate crabs in Northwest Europe. On June 6th, 1944, approximately 70 crabs touched down on Gold, Juno, and Sword beaches with the assault waves. The first landings hit Golden Sword around 0725 with Juno following shortly after as timing slipped by sector and seastate.
The Westminster Draons alone embarked with 56 crabs, 26 standard Shermans, three armored recovery vehicles, and 13 scout cars. Each landing craft tank carried a breaching team of six vehicles, a mix of crabs and AVRE tasked with blasting lanes through German defenses. The plan called for crabs to clear eight lanes on each beach, allowing follow-on forces to push inland before the Germans could recover from the initial bombardment.
The conditions that morning were far from ideal. Rough seas swamped some landing craft and threw others off course. Several crabs drowned before reaching the beach when their craft grounded too far offshore. Others arrived at the wrong sectors and had to navigate under fire to reach their assigned breach points.
But enough got through. One account attributed to German defender Private Martin of the 726th Infantry Regiment described watching crabs approach Gold Beach. He described seeing a Sherman emerge fitted with a revolving drum held by two girders carrying a large number of heavy chains. The drum was spinning and the chains crashed onto the earth with a deafening noise raising clouds of dust and soil.
Several times, he noted, a chain came loose after a mine explosion and flew up into the air a great distance. The psychological effect on defenders watching this mechanical monster advanced through their carefully laid minefields must have been profound. Results varied by sector, but the overall pattern was clear. On Gold Beach, lanes five and six were cleared within 15 to 22 minutes of landing despite the breach commander’s crab being hit and destroyed on the landing craft ramp.
Major Stan dismounted from his burning vehicle and directed traffic on foot under heavy machine gun fire, earning the military cross. Sergeant Lindseay flailed the first path onto the mainland, then supported the attack on La Hamill until his crab was destroyed by anti-tank fire. He received the military medal.
A report issued one week after D-Day documented that crabs managed to clear more than 50% of required exit lanes and used their guns to considerable effect in direct support of infantry. By June 8th, Westminster Dragoon’s B Squadron had only three of 13 crabs fully operational with five beyond repair, but the lanes were open. The American experience at Omaha Beach became the war’s most controversial comparison.
General Omar Bradley, commanding First United States Army, declined most of Hobart’s funnies after demonstrations earlier that year. His official reasoning cited the logistical complications of accepting Britishes vehicles built on Churchill tank chassis, which would require retraining crews and establishing separate supply chains for spare parts.
This explanation has been questioned ever since. The Sherman crab was built on American tanks, not Churchills, eliminating the spare parts argument entirely. Correspondence shows Bradley actually requested 25 flail tanks and 100 crocodile flame tanks after watching the demonstrations. These requests were never fulfilled, possibly due to British production constraints rather than American reluctance.
Some historians suggest deeper institutional resistance. One American staff officer reportedly noted that the general saw it as an infantryman’s battle. Whatever the reasons, at Omaha, American forces landed without crabs, without Avre, without crocodiles. 27 of 29 swimming DD tanks sank in rough seas before reaching shore, leaving infantry with almost no armored support.
They faced minefields and fortifications with rifles, grenades, and extraordinary courage. Casualties reached over 2,000 with more than 1,000 killed. Bradley privately told Montgomery that he considered evacuating the beach entirely during those first desperate hours. The contrast with British beaches was stark. On Gold, Juno, and Sword, crabs and other funnies cleared lanes, filled craters, bridged obstacles, and supported infantry with direct fire.
Casualties were significant but manageable. The beach heads were secured on schedule. Would specialized armor have reduced casualties at Omaha? Likely. Would it have solved Omaha by itself? Not necessarily. Terrain, defenses, seastate, and command friction all mattered. But the correlation between Funny’s deployment and beach clearance success was noted immediately in afteraction reports.
By mid July 1944, First United States Army had finally received nine crab tanks and organized three specialist armor battalions equipped with flails. The post D-Day adoption validated the concept, but the timing raised questions that historians still debate. Beyond the beaches, Crabs supported operations throughout the campaign.
During Operation Goodwood in July 1944, engineers cleared 14 gaps overnight with 79th Armored Division Support. The Westminster Dragoon’s war diary noted that by June 10, approximately 50% of all flail chains needed replacement. German wooden cased holds mines proved particularly problematic. Testing found only 25% detonated when buried in soil.
Their wooden construction absorbing flail impacts better than metal cases. At Overloo in October 1944, Lieutenant Sam Hall’s troop engaged a panther tank while supporting the Cold Stream Guards. The following month at Brookhusen, Hall’s own crab was destroyed by a Panzer Foust. This vehicle now stands in the Overoon War Museum, still bearing its battle damage.
Germany’s attempts at mechanical mine clearing produced spectacular failures. The VSKFZ 617 Minen Roy was a bizarre three- wheeled vehicle with its hull mounted high on tracked wheels for blast deflection. It proved impossibly clumsy at trials, sinking into soft ground and presenting an enormous target. The Cry Roya S was even more impractical, a 130 ton behemoth that never left its development facility before American forces captured it.
Germany recognized the flail concept’s potential, demonstrating the Dresfleg at Kumasorf in January 1945, but by then the war was lost. The Soviet PT34 mine roller was simpler but limited. Rollers could push mines downward rather than detonating them and covered only track width rather than full vehicle width. Comparative studies suggest flails achieved 50 to 100% clearance rates depending on conditions.
Manual clearance remained most thorough but lethal. Postwar mine clearing in Denmark used German prisoners of war to remove over a million mines by hand. The casualty rates were grim with well over a hundred killed and many more injured, demonstrating exactly what the crab was designed to prevent.
Captain Dutis received £13,000 from the Royal Commission on awards to inventors in 1948 with nine colleagues sharing an additional £7,000. Significant recognition for a concept that saved countless lives. The Sherman Crab established mine flailing as a permanent military engineering technique. Every modern flail vehicle traces its lineage to due to its patent and Hobart’s implementation.
The concept did not die in 1945. Modern armies still deploy mine clearing vehicles and Ukraine has received western systems like the Wizant one for breaching modern mine belts. The British developed Arvar has served with American forces in Afghanistan. Croatian remotec controlled flails represent the latest evolution. Unmanned vehicles eliminating crew risk entirely.
Surviving Sherman crabs can be viewed at the tank museum in Boington, the Overoon War Museum in the Netherlands, and military collections in Israel, Canada, India, and Pakistan. Actor Ian Carmichael, later famous for playing Lord Peter Whimsy, commanded a troop of Bqu Squadron 22nd Draons crabs that landed on Juno Beach on D-Day. The crab was never perfect.
It could not fire while flailing. It missed a quarter of wooden mines. It crawled at walking pace through blinding dust. It required constant chain replacement with crews noting that some vehicles needed new chains after dealing with just 40 mines. The noise was deafening. The dust clouds gave away positions to enemy observers, and a broken chain flying loose could injure nearby infantry.
But 43 chains spinning at 142 revolutions per minute kept crews alive inside armor while doing a job that otherwise killed engineers by the hundreds. The 22nd Draons alone lost 34 men killed during the Normandy campaign. The first Lotheians and Border Horse finished the war with 17 killed, 90 wounded, 16 missing, and 36 crabs destroyed.
Heavy losses by any measure. But compare that to the grim casualty rates among German prisoners who cleared Danish minefields by hand after the war. And the value of mechanical clearance becomes undeniable. That machine, which looked insane in 1943, beat German minefields to death across Normandy through France into Germany itself.
British engineering solved a problem that defeated every other approach. Not with elegance, not with subtlety, with chains and brute force, and the simple understanding that sometimes the best solution to a deadly obstacle is to beat it into submission.
