Purpose of this blog

Dmitry Yudo aka Overlord, jack of all trades
David Lister aka Listy, Freelancer and Volunteer

Sunday, February 14, 2021


In 1943 the Allies were well advanced with their plans to return to the continent, however, one problem still remained: How to defeat the masses of concrete the Germans were frantically pouring into their defences. The way the British went about working out how to attack these obstacles was uncharacteristically slapdash. By 1943 there was a general understanding that an armoured engineering vehicle was needed, however, the official project was based around a pair of 4x4 lightly armoured trucks. It was left to unofficial sources to study the problem. One thing that quickly occurred to these pioneers was the need to project a large explosive charge some distance to blow up obstacles. Ultimately Lieutenant John James Denovan would win this race, with Stewart Blackers help, with the Petard spigot mortar. However, the task of creating an anti-obstacle gun was also tackled by Imperial Chemical Industries (ICI) and the gun they created is often mentioned in passing, but no one has had a really good look at it. I am of course talking about the Ardeer Aggie.

ICI had actually done some work with a recoilless rifle beforehand. This 3.5in weapon had been developed to fill a similar role to that of a PIAT, namely infantry anti-tank. It is not recorded how the recoilless effect was achieved. The recoilless rifle known as Aggie worked on the Davis principle of ejecting a counterweight. The very first version of the weapon was a colossal 14in in calibre. It used a primitive black powder charge to propel the projectile. The choice of black powder did actually make sense as ICI felt the weapon needed certain characteristics in its internal ballistics. These were being easy to ignite, having a short all burnt time, but producing a low pressure. This monstrous cannon was actually built, but performance was terrible. The muzzle velocity was just 420fps and the shot tumbled in flight. To make matters worse the black powder charge caused the smoothbore barrel to become horribly fouled to such an extent it needed cleaning out after every shot. There were other problems too. The combined round of projectile, charge and counterweight came in at a hefty 224lbs.The massive weight, and that all three parts were loaded separately, meant that few rounds would be able to be carried, and rate of fire was slow. Finally, there were questions about the ease of manufacturing 14in barrels, or the highly complex fuse needed. The 14inch version was dropped, and design efforts focused on a 10.5in version. 

The 10.5in weapon on its 6-pounder chassis.

This smaller calibre had the advantage that tubes were of a standard size and easier to obtain. Equally, the complete round only weighed in at about 158lbs which was still rather heavy. Things went a little wrong when one considers these came pre-assembled inside a packing tube which was needed as part of the loading process. Equally, should the round misfire there was no means of extracting the round. The round consisted of a canister with a slightly modified No152 fuse, the same fuse as a 3-inch mortar. At the base of the canister was a tail unit which was streamlined down to a drum tail. The tail contained the 3lb cordite charge, of which about 8% of its weight was added potassium nitrate to create the needed characteristics. The charge was fired electrically, with a plug that needed wiring into the gun during loading.

The projectile weighed in at 65lbs, of which 33lbs was the explosive filler. As the projectile was acting as a HESH round it needed to be filled with a plastic explosive. In the first version of the shell Nobels 808 was used, this was found to be very shock sensitive and would prematurely explode on impact. So, the least sensitive plastic explosive that could be found was employed. This was Nobels 851, filling type E. This consisted of the explosive Pentolite melted in a steam-jacket heated pot. Into this was mixed Nitrocotton, Carbamite and Dibutyl Phthalate. The last substance name makes me wonder if scientists aren’t just trying to mess with English speakers as I just can’t get my mouth round the word!

This 10.5in weapon was mounted on a modified 6-pounder gun chassis. The first firing was on the 15th December 1943. In a series of trials, it proved perfectly accurate, able to land five shots into a 3ft circle at 300 yards, and 4ft at 400 yards. Later trials held in January 1944 were conducted in a snowstorm, even then the accuracy was maintained. However, the performance of the explosive filler was poor. The newly proposed explosive filler was the rear two thirds of the warhead filled with 23lbs of RDX/TNT mixture, while the front third was filled with PE No.2.

With this in hand development continued, the next idea was, frankly, utterly bonkers. ICI started to develop a multiple mount for the weapon. The first such design had a colossal eight barrels. These were designed to be fired in either a volley or in a ripple salvo. The first firing on 10th February 1944 was of just four barrels in a volley to see if the mount could withstand the forces involved. It seemed to perform perfectly, so a volley of all eight barrels was fired. Projectiles went everywhere, it was soon discovered that several of the barrels had become misaligned under the recoil stresses. The ICI team took their weapon away and redesigned it. It came back as a six barrelled mounting weighing in at 4.5 tons. The first rounds fired from it on 9th March 1944 scattered wildly, with some rounds landing up to 18ft away from the aim point. Inspection showed the barrels were still in alignment. It was suspected that the projectiles were causing mutual interference between each other. So, the trial was repeated with a ripple salvo, with half a second between each discharge. The Aggie performed perfectly. The mount was designed so that two such mounts could be fitted to the front of a Landing Craft, Tank (LCT). 

LCT's, usually the hold would carry five tanks, in two rows of two, and the last at the front. f you replace that fifth one with the Aggie mount you can see what the thinking was.

This of course raises a question. If, as seems to be the case, the LCT would have its front position occupied by two of these massive weapons, what would happen to the tanks behind them when the counterweights are fired. A series of trials were carried out on the effect of the counterweight. The counterweight took the form of a waxed cardboard tube that was designed to disintegrate about 20-30 yards behind the rear barrel. This tube was filled with sand and weighed 58lbs. It was found this would dent metal plate, so a tank was parked behind the Aggie and was struck by the counterweight. Although the tank was not damaged, it was rendered unusable due to the massive amount of sand dumped on it. Further experiments showed that a wooden board surrounded by a pile of sandbags would stop the containers. Furthermore, they would slowly be demolished enough to allow the tanks to easily drive over them. The idea seems to be to erect this barrier behind each six-barrelled mount on the LCT, drive onto the beach, ripple fire the Aggie’s, which would destroy the sandbag barriers, allowing the tanks to land ashore. 

The Churchill Mk.III Aggie

By now it was April 1944, and the Petard was in service. However, the War Office was looking to the future and was interested in what would come after the Petard. ICI shrunk the Aggie down to 9.5in and managed to fit it to a Churchill Mk.III. This calibre was chosen as it was the largest possible that could be fitted to the tank. Even then the tank was horribly crowded with mechanicals to operate the gun. In addition, the large round would be difficult to load or store multiple rounds of. Finally, there were several complaints about the layout, not least of all the 9in hole in the back of the armour leading directly into the crew compartment. All these complaints were exposed over several months of evaluation at the Land Assault Wing. A provisional list of fixes was issued; however, these do not seem to have gone anywhere. By September it was decided that it would take six months to even begin fitting the weapon, never mind the time span afterwards until the weapon would become available for the service. It would therefore miss the fighting in Europe. Equally, the weapon was objectionable on so many levels no one wanted to put it into service. There was some merit seen in the projectile and a study was undertaken to see if a 9.5in smoothbore howitzer could be made to fire the shell. Fitting this to a Churchill proved very difficult and was abandoned. At the same meeting as the report on the 9.5in howitzer it was proposed to start anew from scratch. They also looked at a new weapon that had just been designed by Major Millis Jefferies of MD1. It was a 7.5in howitzer. In time the new project would become the 6.5-inch breech loading Mk.1 that was fitted to some Churchill AVRE’s after the war. If you want to know more about that weapon, or its contest with the 7.5in weapon, then you can always check out my last book


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Image credits:

tanks-encyclopedia.com and Ed Francis