FEW CAN HAVE MISSED this year’s media coverage of events marking the 70th anniversary of the D-Day landings in Normandy on 6 June, 1944. As a former Minewarfare & Clearance Diving Officer in the Royal Navy, I watched and read with particular interest, but noticed that no mention was made of the fact that the first men ashore on D-Day were frogmen.
In the cases of the British Gold and Silver beaches and the Canadian Juno beach, these frogmen belonged to the 10 RN and Royal Marines Landing Craft Obstacle Clearance Units (LCOCUs).
Pronounced “lock-yews”, these are mistakenly referred to in some sources as “Obstruction Clearance Units”.
In the cases of the American Omaha and Utah beaches, the equivalent of the LCOCUs were the US Naval Combat Demolition Units (NCDUs), but these were not equipped for diving, or indeed swimming, because they assumed that all the obstacles would be exposed at low tide.
The Germans defending the Normandy coast were determined to prevent any Allied amphibious invasion forces reaching the shore, because doing so would reduce their problems considerably.
However, intelligence about their defensive measures had been gathered from local sources as well as aerial reconnaissance and the courageous exploits of the Combined Operations Assault Pilotage Parties, operating from small boats deployed by submarines.
Apart from laying sea mines in the deeper waters offshore, the Germans had constructed four layers of defence in the shallow waters off the beaches:

  • The outermost layer, around 250m to seaward of the high-water line, consisted of a row of “Belgian Gates” (Element C), each comprising 2.5 tons of steel girder and resembling a massive picket fence and rampart.
  • Inshore of this, around 220m out, was a row of seaward-pointing logs driven into the sand. Many of these were capped with mines.
  • Further inshore, at around 180m, was a row of heavy wooden ramps sloping up towards the shore and designed to capsize or sink landing craft.
  • Finally, a loose line of six-pointed “Czech Hedgehog” anti-tank obstacles, constructed from lengths of steel girder, was established closest inshore, around 150m to seaward of the high-water line.

Most of these obstacles were festooned with contact mines or improvised explosive devices using obsolete artillery shells and other munitions.

THE LANDINGS WERE scheduled to start midway between high and low water
with the tide flooding. This meant that the clearance of obstacles could be achieved at a time when a good number of them would be exposed.
The officers and men tasked with the job were drawn from both the Royal Navy and Royal Marines. Almost all were “hostilities only” personnel, with the naval officers coming from the Royal Naval Volunteer Reserve.
In peacetime, they had been bank clerks, cotton salesmen, engineers, carpenters, students and so on.
The LCOCUs were based at HMS Appledore, a Combined Operations Experimental Base on the coast of North Devon. This was shared by the US Navy as an Advance Amphibious Base. Recruitment began in January 1944.
The officer in charge of training was Lt Cdr E C Davis RNR, formerly of the Boom Defence Commandos. He was assisted by Chief Petty Officer D P Reid, a former Merchant Navy boatswain. Between them, they supervised about 20,000 dives.
The Admiralty had already developed the necessary rubber swimming suits for other naval divers, including the crews of X-Craft miniature submarines and Chariot two-man human torpedoes.
A Type C or Type D rubber hood incorporating a relief valve on the top was worn. The triangular fins were based on those used by Italian frogmen during their human-torpedo attacks on shipping at Gibraltar, Alexandria and Malta.

AN ADDITIONAL FEATURE for LCOCU personnel was a kapok-padded undersuit that provided some protection from underwater explosions. One of my friends, the late Lt Cdr Robbie Robinson MBE RN, owed his life to this garment.
He had previously been involved in clearing obstacles from the beach approaches for the disastrous raid on Dieppe in August 1942. At Normandy he survived, although he was nearly “filleted” (his own word) when a German shell exploded in the water near him.
A Royal Engineer Sapper, further from the explosion but lacking the protection of a kapok undersuit, was killed outright.
LCOCU candidates were first sent to HMS Dolphin, the submarine base at Portsmouth. Here they were subjected to diver testing, including being compressed to 9m in a dry chamber and undergoing a simulated submarine escape in the 30m tank, before being trained to use the ubiquitous Davis Submerged Escape Apparatus (DSEA).
The newly developed Siebe Gorman Amphibian Mk IV was trialled but the units finally settled on were the Dunlop Underwater Swimming Breathing Apparatus (UWSBA).
All of these sets were oxygen rebreathers, but the Amphibian Mk IV was particularly popular because it was the first set to have a reducer.
This provided a constant mass flow of oxygen at 1.1 litres per minute, whereas the other sets required the diver to crack open the bottle valve periodically to replace oxygen in the breathing bag as it was consumed.
If the Amphibian-wearer needed extra oxygen for any reason, he could open a bypass valve to reinflate his counterlung immediately.
This set had a single oxygen bottle mounted across the stomach and lead weights high on the back of the harness. A single hose led to the CO2 absorbent container tucked away inside the front of the apparatus.
In the absence of a separate hose for expiration, this required deep “pendulum” breathing to ensure that the expired gas re-entered the counterlung after each breath.
The UWSBA had two vertically mounted oxygen bottles on the front of the harness, separated by large flat lead weights across the stomach.
Its counterlung or breathing bag was mounted across the chest as with the DSEA but, like the Amphibian Mk IV, it had lobes extending level with the ears.
Carbon dioxide absorbent was contained in a large cylinder across the back of the shoulders. A circular full-face mask was fitted with a mouthpiece and spit cock connected by twin corrugated rubber hoses, one of which led to the counterlung on the right shoulder for inhalation while the other led over the left shoulder to the CO2 absorbent container for exhalation.

THE AMPHIBIAN MK IV and UWSBA were the first diving sets designed specifically for horizontal swimming. They were based on confirmatory work performed for the Admiralty at the National Institute of Medical Research by Drs Sands and Paton.
These scientists determined the maximum resistance, expressed in millimetres head of water, that could be tolerated by divers in all postures under water without interfering with normal respiration. The ideal position for the breathing bag relative to a diver’s ear was named the Eupnoeic depth, and it was shown how this depth varied with the depth of respiration.
By designing the breathing set so that the Eupnoeic depth was never exceeded under any conditions, the best possible breathing conditions were achieved.
If you imagine being on the surface while trying to inflate a submerged party balloon subject to the greater pressure of the water surrounding it, you’ll get the idea.
Personnel were then sent to HMS Volcano at Holmrook Hall near Ravenglass in what is now Cumbria to be trained in the necessary explosive demolition techniques.
For example, Element C, attributed to French General Léon-Edmond de Cointet de Fillain to bolster the Maginot Line, had to be destroyed using 36 small charges carefully placed at specific positions on the structure.
When these were detonated simultaneously, no part of the structure would remain more than 45cm proud of the seabed.
Trained personnel then returned to HMS Appledore , where their diving and demolition techniques were rigorously practised, ready for the big day.
They also occupied their time with lessons in unarmed combat; running the five miles between Appledore and Bideford; 20-mile speed marches; scaling the walls of nearby Torrington Castle undergoing various exercises; and dive-training in the saltwater baths of Ilfracombe.

ON D-DAY, four Royal Navy and six Royal Marine LCOCUs, each comprising an officer and 11 men, were deployed from LCAs (Landing Craft (Assault)) at H-Hour.
LCOCUs 3, 4, 9 and 10 were assigned to Gold Beach, 7 and 8 to Sword, and 1, 5, 11 and 12 to Juno. Operating from inflatable boats, they were responsible for clearing obstructions in depths between 3m and 1.4m, while the Royal Engineers had the job of clearing shallower areas and the beach itself.
Despite coming under artillery and mortar fire and being shot at, the LCOCUs succeeded in clearing thousand-yard-wide gaps in the offshore defences before helping the Royal Engineers with their tasks. By the end of the day, they had cleared 2500 obstacles at the cost of Acting Leading Seaman Allister Austin (LCOCU 3) being killed and several other divers wounded, some seriously.
For “gallantry, skill, determination and undaunted devotion to duty during the initial landings on the coast of Normandy”, Lieutenants Robert Billington, Harold Hargreaves and John Taylor of the Royal Naval Volunteer Reserve were awarded the Distinguished Service Cross. Lt David Cogger RM was awarded the Military Cross.
Royal Marine Sergeants Keith Briggs and Peter Jones, Petty Officers Sydney Eagles and George Lock, Leading Seaman Frank Livingstone and Marine Eric Deans were awarded the Distinguished Service Medal.