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Plastic armour (also known as plastic protection) was a type of
vehicle armour Military vehicles are commonly armoured (or armored; American and British English spelling differences#-our, -or, see spelling differences) to withstand the impact of Fragmentation (weaponry), shrapnel, bullets, Shell (projectile), shells, Rocke ...
originally developed for
merchant ship A merchant ship, merchant vessel, trading vessel, or merchantman is a watercraft that transports cargo or carries passengers for hire. This is in contrast to pleasure craft, which are used for personal recreation, and naval ships, which are ...
s by
Edward Terrell Edward Terrell (1902–1979) was a British Liberal Party (UK), Liberal politician, a successful barrister and magistrate with a flair for invention; by 1940 he had registered a number of patents relating to pens, ink bottles and peeling knives ...
of the
British Admiralty The Admiralty was a Departments of the Government of the United Kingdom, department of the Government of the United Kingdom that was responsible for the command of the Royal Navy. Historically, its titular head was the Lord High Admiral of the ...
in 1940. It consisted of small, evenly sized aggregate in a matrix of
bitumen Bitumen ( , ) is an immensely viscosity, viscous constituent of petroleum. Depending on its exact composition, it can be a sticky, black liquid or an apparently solid mass that behaves as a liquid over very large time scales. In American Engl ...
, similar to
asphalt concrete Asphalt concrete (commonly called asphalt, blacktop, or pavement in North America, and Tarmacadam, tarmac or bitumen macadam in the United Kingdom and the Republic of Ireland) is a composite material commonly used to surface road surface, roads ...
. It was typically applied as a casting ''in situ'' in a layer about thick on to existing ship structures made from mild steel or formed in equally thick sections on a
steel Steel is an alloy of iron and carbon that demonstrates improved mechanical properties compared to the pure form of iron. Due to steel's high Young's modulus, elastic modulus, Yield (engineering), yield strength, Fracture, fracture strength a ...
plate for mounting as gun shields and the like. Plastic armour replaced the use of concrete slabs, which although expected to provide protection, were prone to cracking and breaking up when struck by armour-piercing bullets. Plastic armour was effective because the very hard particles would deflect bullets, which would then lodge between the plastic armour and the steel backing plate. Plastic armour could be applied by pouring it into a cavity formed by the steel backing plate and a temporary wooden form. Production of the armour was by road construction firms and was carried out in a similar way to the production of road coverings, the organization of the armouring being carried out by naval officers in key ports.


Development

In August 1939, the
British Admiralty The Admiralty was a Departments of the Government of the United Kingdom, department of the Government of the United Kingdom that was responsible for the command of the Royal Navy. Historically, its titular head was the Lord High Admiral of the ...
had considered the possibility that merchant ships might be attacked by aircraft with machine guns and cannon. No armour plate could be spared to protect the ships' bridges and gun positions, so the Admiralty recommended that ship owners fit concrete paving slabs in layers up to thick to protect the vulnerable crew. The Admiralty had done no testing with armour-piercing bullets, and when the fighting started in earnest, it became evident that concrete armour was almost useless against German machine-gun fire. As the fighting in the
English Channel The English Channel, also known as the Channel, is an arm of the Atlantic Ocean that separates Southern England from northern France. It links to the southern part of the North Sea by the Strait of Dover at its northeastern end. It is the busi ...
intensified in August 1940, casualties rose and the prospect of a collapse in morale threatened.
Edward Terrell Edward Terrell (1902–1979) was a British Liberal Party (UK), Liberal politician, a successful barrister and magistrate with a flair for invention; by 1940 he had registered a number of patents relating to pens, ink bottles and peeling knives ...
was a successful
barrister A barrister is a type of lawyer in common law jurisdiction (area), jurisdictions. Barristers mostly specialise in courtroom advocacy and litigation. Their tasks include arguing cases in courts and tribunals, drafting legal pleadings, jurisprud ...
and
magistrate The term magistrate is used in a variety of systems of governments and laws to refer to a civilian officer who administers the law. In ancient Rome, a '' magistratus'' was one of the highest ranking government officers, and possessed both judi ...
with a flair for invention; by 1940, he had registered a number of patents relating to pens, ink bottles, and peeling knives. When war came, he volunteered for the
Royal Navy Volunteer Reserve The Royal Naval Reserve (RNR) is one of the two volunteer reserve forces of the Royal Navy in the United Kingdom. Together with the Royal Marines Reserve, they form the Maritime Reserve. The present RNR was formed by merging the original ...
and when he was accepted, he was commissioned as a lieutenant in the Special Branch of the Volunteer Reserve, the highest possible rank permitted by fleet orders under the circumstances. Terrell was brought into the Admiralty to run an information-gathering section, concerned with the manner in which small ships were attacked by aircraft. Terrell collected reports and gathered a library of film showing attacks on ships. When visiting damaged ships, he found bridges and chartrooms riddled with bullet holes and sections of concrete in shattered pieces. He also saw dried blood. These grim scenes made a deep impression on Terrell. In August 1940, one of Terrell's staff, Lieutenant-Commander Lane, brought to his attention a report by a shipwright, Lieutenant Hindmarsh. The report had been written in July, about events the previous month during the
Dunkirk evacuation The Dunkirk evacuation, codenamed Operation Dynamo and also known as the Miracle of Dunkirk, or just Dunkirk, was the evacuation of more than 338,000 Allied soldiers during the Second World War from the beaches and harbour of Dunkirk, in the ...
. A
paddle steamer A paddle steamer is a steamship or steamboat powered by a steam engine driving paddle wheels to propel the craft through the water. In antiquity, paddle wheelers followed the development of poles, oars and sails, whereby the first uses were wh ...
had been hit by shells and bullets, but with remarkably few casualties. A marginal note read: Terrell found that the worn-out ship had been heavily caulked with Insulphate, a slightly elastic compound of
asphalt Asphalt most often refers to: * Bitumen, also known as "liquid asphalt cement" or simply "asphalt", a viscous form of petroleum mainly used as a binder in asphalt concrete * Asphalt concrete, a mixture of bitumen with coarse and fine aggregates, u ...
filled with small bits of cork. Insulphate was a popular solution to the problem of coping with the flexing of a ship that was old or that was now being used in waters rougher than those for which she was originally designed. Lane suggested that the mastic might have protective properties. Terrell agreed and immediately made an appointment to see the manufacturers, Durastic Bituminous Products Ltd. By 17 August 1940, he had samples for testing.Terrell, 1958, p45-56. Just two days after receiving his first samples, Terrell tested them at a
rifle range A shooting range, firing range, gun range or shooting ground is a specialized facility, sports venue, venue, or playing field, field designed specifically for firearm usage qualifications, training, practice, or shooting sport, competitions. ...
at the Road Research Station, Harmondsworth. The results were disappointing; bullets went straight through the soft material and through a mild steel backing plate. Disappointed, some of the scientists witnessing the tests left. William Glanville, head of the station, stayed and the men performed a few more test shots. In the resulting discussions, Terrell suggested replacing the cork with rock to deflect the hard core of an armour-piercing bullet so that it hit the backing plate at an angle, dispersing its energy so that it would not penetrate. Terrell recalled an old legal case that he had conducted for the Amalgamated Road Stone Corporation. While studying background technicalities, he had visited Penlee Quarry at
Newlyn Newlyn () is a seaside town and fishing port in south-west Cornwall, England, United Kingdom.Ordnance Survey: Landranger map sheet 203 ''Land's End'' It is the largest fishing port in England. Newlyn lies on the shore of Mount's Bay and for ...
in
Cornwall Cornwall (; or ) is a Ceremonial counties of England, ceremonial county in South West England. It is also one of the Celtic nations and the homeland of the Cornish people. The county is bordered by the Atlantic Ocean to the north and west, ...
, where he was told that Penlee granite was the hardest available. Terrell, who owned shares in the company, went on to insist that Penlee granite be used for plastic armour, whatever its material qualities. Terrell had new targets made to his specifications by Durastic Bitumious Products. The new targets, with a variety of sizes of granite chips and proportions of mastic and
limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...
, were delivered on 20 August. Testing was performed two days later and supplies of granite started to arrive at the Road Research Station for more trials. Terrell's choice of the Road Research Station for a firing range was convenient, as they had all the necessary experience with dealing with stone and bitumen – though in his memoirs, Terrell insists that the original choice was simply good fortune. Terrell coined the term "plastic armour" for his invention, partly because it was plastic in the sense of being malleable and ductile while hot, but also because he thought that the term might be confusing to German intelligence, who might assume that the product was made with the synthetic wood plastics then available. On 27 August, Terrell, Glanville and a Lee drafted a report detailing their efforts and giving a recipe for plastic armour; the entire development cycle had taken just 10 days. The recipe required 55%
granite Granite ( ) is a coarse-grained (phanerite, phaneritic) intrusive rock, intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly coo ...
, 38% limestone, and 7% bitumen; it was important that the stone was carefully graded and free from grit. The backing plate was vital; it would usually be thick mild steel. Since this was from what vital parts of a ship's superstructure were made, it was possible to cast plastic armour'' in situ'' between existing plates and temporary wooden shuttering, usually to a thickness of . Where this was not possible, armoured plates could be factory made. Wooden backing could also be used when nonmagnetic protection was needed near the ship's compass. The war had brought road building to a virtual halt, so plenty of suitably qualified workers and machines were available for the task of armouring Britain's ships. Plastic armour was at first met with resistance from some senior officers. Terrell soon received enthusiastic support from the Admiralty Trade Division, which was responsible for protecting
convoy A convoy is a group of vehicles, typically motor vehicles or ships, traveling together for mutual support and protection. Often, a convoy is organized with armed defensive support and can help maintain cohesion within a unit. It may also be used ...
s and their ships. To proceed in an orderly manner, the Trade Division needed the approval of the Admiralty's Department of Naval Construction (DNC). Terrell and the chief of the
Directorate of Miscellaneous Weapons Development Directorate may refer to: Contemporary *Directorates of the Scottish Government * Directorate-General, a type of specialised administrative body in the European Union * Directorate-General for External Security, the French external intelligence a ...
(DMWD), Commander Charles Goodeve, met with representatives of DNC, who rejected plastic armour out of hand. DMWD performed a series of independent tests at the Royal Navy shore establishment HMS ''Excellent'', resulting in a positive report: The report was forwarded to the DNC, but was rejected again. Some within the navy objected to the use of the word ''armour'' to describe a mixture derived from road-building materials. The DNC said that it would remove its objections provided the word "armour" was removed from the name of the product. The Trade Division insisted that the term "armour" was important for morale and that at this stage higher authorities decided that the DNC would be bypassed and production would start without their formal approval. The process and specification was patented secretly under an agreement that the British Crown had full use of the invention. Glanville insisted "in good faith" on his name appearing in the patent; Terrell acquiesced so the armour could be put into use without delay. Plastic armour was available in large quantities and cost only per ton – compared with heat-treated armoured plate at about £150 per ton and in short supply (though weight-for-weight somewhat more effective than plastic armour). Plastic armour went into full production in October; facilities were soon in place in every major port involving every major road-building contractor in the country. Word spread abroad to Britain's allies. By the end of the war, plastic armour had been fitted to some 10,000 ships. Plastic armour was even used on the fighting ships of the Royal Navy, although in these cases the Department of Naval Construction insisted on referring to it as "plastic protection". Development and testing continued. Eventually, the bitumen of the original formulation was replaced by less expensive pitch and the Penlee granite was replaced by flint gravel. Elsewhere in the world, people used whatever stone was available. Terrell invented the Scorpion, a plastic armoured vehicle apparently similar to the
Armadillo armoured fighting vehicle The Armadillo was an extemporized improvised armoured fighting vehicle produced in Britain during the invasion crisis of 1940–1941. Based on a number of standard lorry (truck) chassis, it comprised a wooden fighting compartment protected by ...
. Also, a semiportable pillbox or strongpoint made of prefabricated panels of plastic armour was made for the
Home Guard Home guard is a title given to various military organizations at various times, with the implication of an emergency or reserve force raised for local defense. The term "home guard" was first officially used in the American Civil War, starting ...
and was considered as a means of covering the retreat of the
commandos A commando is a combatant, or operative of an elite light infantry or special operations force, specially trained for carrying out raids and operating in small teams behind enemy lines. Originally, "a commando" was a type of combat unit, as opp ...
at the end of the raid on Dieppe. Terrell was appointed to the staff of the
First Sea Lord First Sea Lord, officially known as First Sea Lord and Chief of the Naval Staff (1SL/CNS), is the title of a statutory position in the British Armed Forces, held by an Admiral (Royal Navy), admiral or a General (United Kingdom), general of the ...
and promoted to the temporary rank of commander. After the war, Terrell and Glanville received a patent for plastic armour, after the invention was disputed by the manufacturers of Insulphate and applied to the Royal Commission on Awards to Inventors for their work on plastic armour. The court hearing lasted for a full week, with the Crown protesting that plastic armour had been developed in the normal course of the men's work. If this had been the case, it would have reduced the size of the award. The court found in favour of Terrell as sole inventor, granting an award of £9,500 in recognition of the usefulness of the invention and the initiative with which it was developed. Terrell, in turn, passed some of the award on to Glanville.National Archive. T 166/21 Awards to inventors - Terrell and others. (The award was a considerable sum: £9,500 in 1946 is equivalent to £ in .)


American production

In August 1943, American experiments on the general problem of protection against shaped charges began, and by October of that year, a plastic armour much lighter than the steel armour required for the same amount of protection was found. This armour, made by the Flintkote Company, was improved through a series of tests and a modified armour of pure
quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...
gravel in a mastic of pitch and
wood flour Sawdust (or wood dust) is a by-product or waste product of woodworking operations such as sawing, sandpaper, sanding, Milling (machining), milling and Router (woodworking), routing. It is composed of very small chips of wood. These operations ...
was designated HCR2. Tests were also conducted to test plastic armour's ability to protect ships from
torpedo A modern torpedo is an underwater ranged weapon launched above or below the water surface, self-propelled towards a target, with an explosive warhead designed to detonate either on contact with or in proximity to the target. Historically, such ...
es with shaped-charge warheads, but this project was abandoned due to the low probability of these weapons becoming a serious threat and protection of
armoured fighting vehicle An armoured fighting vehicle (British English) or armored fighting vehicle (American English) (AFV) is an armed combat vehicle protected by vehicle armour, armour, generally combining operational mobility with Offensive (military), offensive a ...
s and concrete fortifications became the priorities.


Tank protection

The original plan for tank protection with plastic armour was to produce HCR2-filled steel panels, small in size to reduce the area damaged by a single projectile, which could be fastened to an
M4 Sherman The M4 Sherman, officially medium tank, M4, was the medium tank most widely used by the United States and Western Allies in World War II. The M4 Sherman proved to be reliable, relatively cheap to produce, and available in great numbers. I ...
in an emergency. To protect against the largest Panzerfaust, 8-12 tons of plastic protection were required for an M4, while an M26 Pershing's greater base armour meant it required only 7.1 tons of additional protection to equal an M4 with 11.7 tons of plastic protection. This was a 34% increase in weight for an M4, but only a 16% increase for an M26, and the panel for the M26's turret was only inches thick compared to inches for the M4. New panels made of welded steel armour, half an inch thick on the sides and three-quarters of an inch thick on the faces, were designed, but their construction was incomplete at the end of World War II. As a result of increasing tank losses to shaped-charge weapons, another type of panel that could enter production in only a few weeks was designed. This new type of panel used -inch mild steel instead of armour steel, and had a two-inch plate of 21ST
aluminium Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...
alloy backing the face plate for reinforcement. One set of this armour was completed and tested just after the end of World War II and was considered quite satisfactory, although less so than the panels made of armour steel.


References


Further reading

* White, Merit P.: ''Effects of Impact and Explosion'', 1946 * * * *


External links

* {{DEFAULTSORT:Plastic Armour Vehicle armour Merchant navy Naval armour Military equipment introduced from 1940 to 1944