The British Army will soon be augmenting its firepower with 515 guns delivered under a £150 million contract announced last July. An innovative design is being used for both the guns themselves and the ammunition they will fire.
The weapon is the 40mm cannon that will arm the army’s new Ajax and upgraded Warrior combat vehicles. Two specific features of the overall system represent the most immediately obvious departures from previous practice.
The first feature is a rotating breech that will allow ammunition to be loaded at a 90° angle to the barrel. The second difference is that the ammunition will not be of the conventional ‘bullet’ type but will instead enclose both the projectile and the propellant in a cylinder with closed ends.
The main consequences of these new features will again be twofold. Inside the vehicle, there will be a more economical use of space that will allow for enhanced storage capacity and ease of movement for the crew. Outside – more precisely, at the point of impact of the projectile and target – there will be up to four times more destructive power than could be imparted by the 30mm ammunition previously used by such light armoured vehicles.
This Cased Telescoped Armament system has been developed by CTA International (CTAI), a joint venture between the UK’s BAE Systems and French company Nexter. According to Craig Fennell, managing director of CTAI, the roots of the venture go back to the mid-1990s, when initial research got under way to address such issues as the optimal calibre for the system.
At that point the participants were the UK’s Royal Ordnance, which was subsequently acquired by BAE, and the French GIAT Industries, which has now become Nexter. Intensive qualification, though, began only in 2008, when the British and French defence purchasing establishments formally selected the 40mm calibre for the weapons system.
Division of labour
Production is now split between the two countries. The ammunition is made at BAE Systems’ munitions sites in Washington in Tyne and Wear and Glascoed in South Wales, while the gun is produced in Bourges in central France at a plant that carries the CTAI name. The Bourges plant, says Fennell, employs 85 people and carries out manual assembly of components provided by a predominantly French supply chain of 25 other organisations. Bourges is also the location for research and development and a test firing range.
Many of the technical challenges involved in making the gun work as intended are met by supplier companies, says Fennell. He mentions, for example, the “extremely tight tolerancing” required by the barrel, chamber and breech. The actual figures are confidential, but he indicates that the demands involved are appreciably more stringent than have previously been the case.
But the most obviously innovative aspect of the gun itself is the rotating breech system that enables ammunition to be loaded at a 90° angle to the barrel. Fennell says this aspect is unprecedented.
The biggest challenge involved in making the system operate well, he says, was ensuring the sealing of the ammunition was as effective as it would be in a conventional configuration. It has to be just as capable as the previous arrangement of ensuring there is no leakage of propellant fumes back into the crew compartment after the gun is fired. He indicates that precisely how this is achieved is the key item of intellectual property that CTAI possesses, and that it must remain secret.
The mechanism of the gun, though, represents only one innovative aspect of the system. The other involves the ammunition, and the way it is stored and fed to the gun.
‘Beer can’ rounds
In appearance, an element of the ammunition is, in Fennell’s words, “rather like an extended beer can”. It is a metal cylinder 65mm in external diameter and 255mm in length that contains both the propellant charge and the 40mm-diameter projectile. A key difference between this type and conventional munitions is that the propellant is located not only behind the projectile but around it, too.
Despite the cylinder being much shorter than a conventional round, this format creates an enhanced propulsive force that, in turn, provides the projectile with an increased muzzle velocity, says Fennell. When the round is fired, the projectile is blasted through the plastic face of the end cap in front of it and up the barrel of the gun. Importantly, he confirms, this means there is no loose metal flying around inside the breech mechanism or gun barrel.
In turn, this external shape for the ammunition facilitates its storage – typically 60 rounds at a time – in a box-like ammunition handling system attached to the side of the gun, with which it is integrated by an onboard computer. The gunner can then select the type of round they wish the gun to fire by entering the details on a keypad, after which an appropriate round will be loaded and fired with an appropriate fuse setting.
Interestingly, the UK Ministry of Defence is sourcing its own ammunition handling system separately from the one developed by CTAI, although the latter will be used by French armed forces. Fennell says that there will be no significant differences
in the capabilities of the two systems.
This approach has several advantages. One is its straightforward compactness and ease of use. As Fennell points out, it entirely obviates the handling problems that can be associated with the manual loading of ammunition in clips or belts.
Mixed magazine
Another advantage of the new design is that it enables different types of ammunition to be stored in the same magazine and selected according to immediate requirements. Armour-piercing and training rounds are already qualified for military service, while an airburst round for use against ground targets and a point-detonating round that can penetrate thick concrete are completing qualification. CTAI is also working on an airburst round for use against airborne targets.
An important factor is that the system enables the breech of the gun to remain empty until a particular type of round has been selected. In contrast, conventional breech-loading systems automatically reload the gun, meaning that it might be necessary to fire off an inappropriate round before the right type of ammunition for the circumstances can be selected.
The advantage for the crew in a combat situation is clear. According to Fennell, the maximum rate of fire attainable is 200 rounds per minute.
Vehicles equipped with the gun should start entering service within the next couple of years. When they do, there should be no doubt, he says, that they will be armed in a way that represents a genuine breakthrough in sophistication and effectiveness.
“Other people have attempted to bring this technology into qualification in the past,” he says. “But no one has ever achieved it – we are the only ones who have a cannon that operates in this way.”