Shooting the War

Artillery Guns of the WWII

Running parallel with this unfolding story of piercing projectiles was the development of the hollow-charge principle into a viable weapon. This illustrates the adaptation of a well-documented scientific phenomenon to a weapon of war: almost 200 years ago a Norwegian engineer had observed that hollowing out the face of an explosive charge made it cut deeper into rock when blasting. In the 1880s an American experimenter, Monroe, found that when firing guncotton slabs against armour plate, the initials ‘USN’ engraved in the guncotton reproduced themselves in mirror-like form in the face of the armour plate. From his observations and reports the phenomenon became known as the ‘Monroe Effect’ and was a scientific curiosity for many years. Just before the First World War one or two inventors toyed with the idea of employing this effect in mines and torpedoes, but since no one really understood why it did what it did, it was difficult to engineer the idea into a practical form.
Just before the Second World War broke out, a Swiss consortium approached the British government to offer a ‘new and powerful explosive’ for anti-tank use—at a high price. The inventors refused to divulge any information until cash was forthcoming, but were prepared to demonstrate their projectile being fired. An astute observer from the Research Department of Woolwich Arsenal went to Switzerland to watch the firing; being a well-read expert on ammunition development and history, he realised that what he was watching was not a new and powerful explosive so much as a practical application of the Monroe Effect. Upon his return to Woolwich he duly reported this, and, since it appeared that the Monroe Effect could be made to work, research immediately began into applying it to a light anti-tank grenade which the infantry soldier could fire from his rifle. Before the outbreak of war, this ‘68 Grenade’ had been perfected and was in production, and carries the distinction of being the first weapon ever to reach the hands of troops which relied on the Monroe Effect, or as it came to be known, the Hollow-Charge Principle.
What is this Hollow-Charge Principle? Put simply, it consists of forming the forward surface of the shell’s explosive charge into a cone or hemisphere and then lining this with a thin metal liner. The shell is then fitted with a suitably shaped nose, for ballistic effect and also to give the vital ’stand-off’ distance. This is the distance from the target—a matter of a few inches—at which the explosive must be detonated in order for the hollow charge to work effectively. On detonating the explosive at its rear end, the detonation wave exerts an immense pressure on the metal of the liner; the cone shape virtually’focusses’the explosive energy and causes the metal of the liner to be shaped into a jet of finely-divided metal and explosive gas, shooting toward the target at speeds of up to 20,000 feet per second. The stand-off distance is necessary in order to allow this jet to form and accelerate. When the jet strikes the target plate, the pressure exerted is so great as to blast a hole through the armour, blowing splinters of metal from the inside and permitting the white-hot jet to pass into the tank where it will set fire to fuel or ammunition, and, of course, kill or injure the crew.
The great virtue of the hollow-charge shell is that its performance is always the same, irrespective of the velocity at which it strikes. Even if the shell were standing still when detonated, the penetration would be the same. Because of this, it could be fired from guns too small to fire the large cartridges needed to give the necessary velocity to normal piercing projectiles. As soon as the 68 Grenade was seen to be successful, design began on other hollow-charge projectiles. A great deal of work went into producing one for the 25-pounder, though in the end it was never issued, since the AP shot issued for that gun was quite satisfactory and there was no real need for a hollow-charge shell. Then came a request from India to produce an anti-tank projectile for the 3.7-inch Pack Howitzer, the modern version of Kipling’s immortal ’screw-gun’. This gun, a small and portable weapon, could not be made to fire a piercing projectile at anything like the velocity needed to defeat even Japanese tanks, and a hollow-charge shell was designed and placed in production. The same shell was used in the 95-mm howitzer, an abortive infantry support gun which never saw service as a towed weapon, though it was employed as a self-propelled support weapon by the Royal Marines in Normandy and by the Armoured Corps.
By 1944, though, sufficient basic research had been done into this principle for it to be seen that a spinning shell was not the ideal method of employing hollow charges, since the spin tended to spread the jet out and give poor penetration. Finned projectiles were more effective, and consequently no more artillery shells were designed around the hollow charge; it was extensively employed, instead, for infantry weapons such as the PIAT, the Bazooka, and a variety of rifle grenades.
The Germans, and later the Russians, embraced the hollow-charge shell wholeheartedly. The Germans began issuing shell in late 1940 and eventually almost every German field and tank weapon had a hollow-charge shell, thus giving every gun or howitzer an anti-tank capability. Indeed, so short were the Germans of anti-tank guns after the Russian invasion got under way, that they hastily collected up all the French army’s 75-mm guns and assembled hundreds of them on to redundant anti-tank gun carriages of German design. A hollow-charge shell was produced and these makeshift weapons were deployed in Russia to stem the advancing Soviet tanks until 75-mm and 88-mm anti-tank guns were in sufficient supply. Judging from appearances, the Soviet hollow-charge shells were developed as virtual copies of German designs which had been captured.
In addition to artillery shell Germany also used the principle for infantry weapons such as the Panzerfaust, rifle grenades, and even a small shell which could be fired from a signal pistol. They also employed the principle in an ingenious attempt to prolong the life of the prewar 37-mm anti-tank gun, whose piercing projectile was, by 1942, no longer effective against current tanks. A large hollow-charge bomb was fitted with a hollow tail carrying fins; within this tail was a stick which fitted snugly into the barrel of the 37-mm gun, allowing the tail and fins to slide over the barrel. A blank cartridge completed the outfit, and this was used to fire the stick bomb to ranges of 300 to 400 yards. The bomb’s warhead was about 6 inches in diameter and carried about 8 pounds of explosive, giving a devastating effect at the target. In all fairness, it must be pointed out that Lieutenant-Colonel Blacker, inventor of the PIAT and the `Black Bombard’ of Home Guard fame, had proposed a similar 60-pound stick bomb in 1940, to be fired from the 25-pounder, but the idea was turned down on the grounds that it might lead to misemployment of the gun as a purely anti-tank weapon. (This misemployment theme was not confined to the British side: many German Flak commanders bewailed the loss of their valuable 88-mm Flak guns as they were whittled away to provide anti-tank defences.)
The third subject is the application of new principles to gun design. The first of these to be unveiled was the taper-bore antitank gun, which has already been touched upon. This was the child of a German engineer called Gerlich, who, advocating his principle of attaining high velocity without attracting any buyers, had been stumping the world for several years. He was briefly employed by both the US War Department and the British War Office at various times, but his ideas on improving shoulder arms were felt to be impractical. He eventually settled in Germany and saw his idea accepted as an anti-tank weapon. The 28/21-mm came first, then a 42/30-mm and finally a 75/50-mm. Unfortunately, the lack of tungsten carbide for the special projectiles spelled the demise of these weapons, but experiments continued with coned bores and coned muzzle-adapters for guns of various calibres up to as large as 280-mm, in order to boost velocity and range. These were intended to use high-explosive shells, which were more practical in the larger calibres, though the development of a shell which would stand up to being squeezed down the gun barrel was no easy task.
The second, and more widespread, new line of thought was the recoilless gun. Like most weapon ideas, there was nothing really new about it: Commander Davis of the US Navy had produced a recoilless (RCL for short) gun during the First World War which was adopted by Britain as an anti-Zeppelin aircraft weapon. The virtue of an RCL gun is that by having no recoil one needs no complicated hydraulic buffer system to absorb the firing shock: one need only make the gun-carriage strong enough to take the weight of the gun, instead of being strong enough to withstand being fired from—an ideal state of affairs for an aircraft weapon, particularly in the stick-and-string era. Davis’s idea is worth looking at, although outside our time scale, since it is the classic recoilless weapon. He simply provided the gun with two barrels, one pointing forward which fired a normal shell, and one pointing rearward which fired an identical weight of grease and buckshot. When the central cartridge was fired the shell and countershot departed at equal speed in opposite directions and cancelled each other’s recoil. From this it can be seen that if you make the countershot (say) one-fifth of the weight of the shell and fire it out at five times the speed, then the gun will still be in balance. Taking this idea to its logical conclusion one finishes up firing out of the back of the gun a fast, light stream of gas, still balancing the recoil since the weight times speed of the gas is the same as the (greater) weight times (slower) speed of the shell.
Cutting down the recoil
This was the principle which the Germans revealed in Crete when their troops appeared armed with a 75-mm RCL gun. The shell was the standard 75-mm shell, but the cartridge case had a frangible plastic base which held for long enough to allow pressure to build up and start the shell moving, then blew out through a hole in the breech-block, releasing the balancing stream of gas. The all-up weight of the gun, on its ex-machine gun tripod, was only 320 pounds, whereas the weight of the standard 75-mm field gun was about 11/2 tons—no mean saving for airborne carriage. A 105-mm version soon followed, weighing 855 pounds as opposed to the 105-mm 1E FH18’s 4,312 pounds, and many more developments began in this field to provide light weapons for mountain troops and infantry, particularly for anti-tank use. (It ought perhaps to be pointed out that the Panzerfaust was in fact a recoilless gun, and not, as generally supposed, a rocket launcher). Eventually RCL guns of up to 380-mm calibre were under development, including many for slinging beneath aircraft to carry artillery aloft for the battle against the Allied bombers, but none of these came to fruition.

n Britain, the RCL gun development during the war is a scarcely-known story of one man’s persistence. Sir Denis Burney, airship designer and prolific inventor-engineer, began to be interested in the recoilless principle early in the war. In order to prove his theories he converted a four-bore gun into a recoilless weapon and proceeded to fire it from the shoulder with ease; it must have been the world’s most comfortable duck gun. Having proved his point he proceeded to design a series of RCL guns ranging from 20-mm to 8-inch calibre. In addition to designing the guns, he expanded his theories and designed special ammunition to take advantage of the ballistic peculiarities of the weapon. He argued that since the rearward blast was taking place, the pressure within the gun would be less than with a conventional type, and the shell would be subjected to a more steady thrust. In which case it would be possible to make shells with thinner walls, which would carry greater charges of explosive than previously possible. He then went further, and reasoned that, since the shell walls were thin, if the shell were to be filled with the then new plastic explosive, it would spread on to the surface of the target like butter; a fuse fitted in the base of the shell would then detonate this plaster and blast in the target. His envisaged target was either the concrete emplacements of the European coast, or the palm-reinforced Japanese bunker, and he called his shell the Mal I buster’.
In 1944 his designs were accepted and a 3.45-inch (the same calibre as the 25-pounder) shoulder-fired gun, a 3.7-inch towed gun, a 95-mm towed howitzer, and a 7.2-inch towed howitzer were prepared for production. The 95-mm was also jeep-mounted—the first application of what has since become a standard method of carrying these guns. The 7.2-inch soon fell by the wayside, since it had been intended solely as a means of defeating the Atlantic Wall emplacements, but other weapons were found to do all that was needed. The 3.45-inch was intended as an infantry weapon in the jungle, enabling one man to carry what was virtually a 25-pounder punch on his shoulder. The 3.7-inch was proposed as the future infantry anti-tank weapon, and the 95-mm was contemplated as the airborne field gun to replace the US 75-mm howitzer and the 25-pounder. However, before the guns were produced in sufficient quantity for issue, the war came to an end; some 3.45-inch and 3.7-inch guns were issued to selected infantry units to obtain their reaction to RCL guns as a general thing, and the 95-mm was abandoned altogether.
The principal difference between the Burney guns and the German type was that the Burneys had much longer barrels, and used cartridge cases which, instead of the plastic blow-out base, used many perforations in the sidewall to release the gas into a surrounding chamber, from whence it was passed back to a number of vents around the breech.
Concurrently with Burney’s work in Britain, American designers began on similar weapons. A 105-mm howitzer T-9 was developed on similar lines to the German 105-mm, having a blow-out base to the cartridge. Another team developed 57-mm and 75-mm weapons which used perforated cases similar to the Burney pattern but having more and smaller holes, and also had the shell driving band pre-engraved in order to reduce the pressure inside the gun. Both these latter weapons were accepted for service early in 1945, saw service with the US Army in the Pacific theatre, and remained in service for many years. A third team, this time under the auspices of the National Research and Development Council, developed a 4.2-inch RCL mortar, an unlikely-sounding weapon which so as to be able to fire direct at the target at low angles, carried a small rocket on the nose of the shell to push it down the barrel’and fire the propelling cartridge in the usual mortar fashion. Due to the blast of the rearward jet, it could only be fired at low elevations; there was a certain amount of enthusiasm for this weapon but it never entered service.
Perhaps the best summing up of all wartime development on RCL weapons was made in a wartime report: ‘Undoubtedly a number of effective recoilless weapons have been developed, but they are being accepted with reserve, and will only be considered as supplementary to older and more orthodox weapons which have proved their accuracy and reliability in service.’
There is, unfortunately, no space here to delve into more recondite stories of research and development: the British 13.5-inch gun linered-down to 8-inch calibre which, fired from Dover, reached a range of over 100,000 yards; the British and American development of flying artillery, which culminated in the mounting of a 32-pounder anti-tank gun in a Mosquito; the German V-3 multiple-chamber gun which was intended to shell London; the American 36-inch mortar ‘Little David’, designed to batter Japanese strong-points; the German rocket-assisted and ramjet-assisted heavy artillery shells which promised vast increases in range; or the Anglo-American development of the electronic proximity fuse which proved the answer to both ‘Doodlebugs’ and kamikaze pilots. These and similar stories may only interest the specialist, but they, together with what has been written here, serve to illustrate the incredible range of inventions brought into play in the war waged between the designers and inventors of each side, each endeavouring to get one step ahead of the other, if only temporarily.