Light AFV guns and the WFLIP project
© Anthony G Williams
Based on a presentation given to the 21st Small Arms and Cannon Symposium held at the Defence Academy of the United Kingdom, August 2007
AMENDED 6 APRIL 2008
The cannon mounted in the turrets of LAFVs (Light Armoured Fighting Vehicles) have two principal uses: one is to engage their equivalents, for which they need guns powerful enough to penetrate their armour when using AP ammunition, while the other is to engage softer targets; unarmoured vehicles, buildings and other cover, and troops.
A gun-armour race has been slowly developing among LAFVs. The previously common 20mm calibre, particularly the 20x139 used in the Rheinmetall Rh 202 among others, has mainly been superseded for this purpose by the 25x137 NATO round, principally in the ATK MK242 Bushmaster Chain Gun, but the 30mm calibre is now standard for almost all new developments. The British 30mm Rarden L21A2 gun (30x170) has of course been in service for decades, as have the Russian BMP 30mm guns (30x165), and these have more recently been joined in service by the Mauser MK 30 and the ATK Bushmaster II (since replaced in production by the marinised MK44 version developed for the USMC's EFV), both in 30x173 calibre. One oddity is the 1950s Soviet 30x210B cartridge, developed for the NN-30 naval gun, which was adopted by Yugoslavia in the 1980s for the Zastava M86 (single ammo feed) and M89 (double feed) AFV guns; this appears to have been revived for new Serbian LAFV developments.
Moving up in power, the 40x365R Bofors L70 has been in Swedish service for some years in the CV9040, and the round is also used by the new Korean Infantry Fighting Vehicle. Less well known in the West is the Japanese use of the 35mm Oerlikon KDE in the Type 89 MICV. The Netherlands and Denmark have also chosen the 35x228 Oerlikon round for their new CV9035 MICV, only this time in ATK's Bushmaster III.
In the 1980s Otobreda of Italy and IMI of Israel co-developed the self-loading 60mm HVMS 60 (High-Velocity Medium-Support) around new 60x410R ammunition. After a while, the two firms parted company and continued separate developments of the gun and ammunition. The only sale achieved so far is by IMI to Chile, to rearm some old tanks (apparently with a manually-loaded version of the gun). At about the same time, Germany also considered the idea of an LAFV armed with a version of the Bofors 57mm, but this went nowhere. The largest conventional cannon currently being promoted is the new Russian AU-220 turret containing a version of the old 57mm S-60 AA gun in 57x347SR calibre. This is initially intended for rearming the PT-76 light amphibious tank but is said to be suitable for other LAFVs.
20x139 (HS 820, US M139, GIAT 20M693, Rh 202), 25x137 (M242 Bushmaster), 30x165 (2A42, 2A72), 30x170 (Rarden), 30x173 (Bushmaster II / MK44, Mauser MK30), 30x210B (Zastava M86/89), 35x228 (Oerlikon KDE, Bushmaster III)
35x228 (Oerlikon KDE, Bushmaster III), 40x364R (Bofors L/70, Bushmaster IV), 57x347SR (Russian AU-220M), 60x410R (IMI / OTO 60mm)
For attacking other LAFVs the ammunition of choice has developed from the APHC (armour piercing hard core) through APDS, and is now APFSDS (Armour-Piercing Fin-Stabilised Discarding-Sabot), effectively a miniature version of the principal Main Battle Tank AP ammunition. The penetrators are almost universally of tungsten alloy, although the USA fields the 25mm M919 DU round; the enhanced penetration which this provides helps to compensate for the relatively low power of the cartridge.
The picture below shows a 35mm APDS (in its sabot, and the flight projectile only) and a 25mm APFSDS.
In current service, the AP ammunition is supplemented by point-detonating fuzed HE for use against soft targets. However, the main focus for development in LAFV ammunition at the moment is airburst HE, using a time fuze.
Several drivers are pushing up the gun calibre of new LAFVs. One of them is that the armour protection of such vehicles is improving, as can clearly be seen as a result of operations in Iraq. The weight of existing LAFVs has been steadily increasing, mainly to add protection: over their lifetime, the M2 Bradley has increased from 23 to 30 tonnes, the Warrior from 25 to 32, the CV90 from 21 (prototype) to 35, the German Marder from 27.5 to 37.5, while the new German Puma weighs in at a massive 43 tonnes. This will require more powerful AP ammunition to achieve reliable penetration in the future.
The need to blow holes in buildings being used as cover also favours larger HE shells. But perhaps even more important is the current interest in airburst HE/fragmentation for attacking enemy forces hiding behind walls and other cover. This is known as HEAB (High Explosive Air Burst) or ABM (Air-Burst Munition). First in the field were modified version of Oerlikon's AHEAD time-fuzed shrapnel ammo, available in 35mm and 30mm calibre. However, this only throws the fragments forwards, which may miss soldiers behind cover. Accordingly, there is more interest in HE/fragmentation shells which can be designed to project fragments downwards and even backwards, as well as forwards. If one of these shells, with a spherical fragmentation pattern, is detonated above a target, then only a small minority of the fragments will strike the targets. In these circumstances, shells big enough to produce a large quantity of fragments are clearly advantageous (especially as the time-fuze systems are very expensive, so maximising the "bang for the buck" is important).
As a result of these issues, the minimum calibre being considered for most new LAFV developments is 30mm. Even that may be considered marginal in the long run, hence the current interest in several armies in 35mm and 40mm armament. This provides a measure of future-proofing; a wise precaution given that once a decision about a new gun calibre is made, it tends to be in service for several decades. It is significant that the Dutch study which led to the decision to select the 35mm calibre concluded that 30mm APFSDS would be inadequate to deal satisfactorily with the latest up-armoured versions of the Russian BMP-3. However, there are practical limitations on gun and ammunition size, especially in vehicles intended to carry troops as well as a gun. Perhaps of most significance is that the fact that many programmes will be to fit – or refit – new armament to existing vehicles, in which case the space available for the turret (and especially the diameter of the turret ring) can impose a significant limitation on the size of the gun and its ammunition feed.
There is therefore a trend to try to squeeze more performance out of existing guns by increasing their calibre. An example of that is the development of the 40mm ‘Super 40’ or 'Supershot', which is basically a necked-out version of the 30x173 case retaining the same rim diameter and overall length as the 30mm cartridge. It is therefore in principle a straightforward task to modify the externally-powered 30mm Bushmaster II gun to take the Super 40 ammunition; it just needs a new barrel and some modifications to the feed unit. A few years ago, General Dynamics Ordnance and Tactical Systems (GD-OTS) were looking at different case lengths for the HE and APFSDS versions of the Super 40, but more recently have been working on a compromise case length for both, of around 190-195mm. An earlier, similar, exercise was to neck out the 35x228 Oerlikon case to create the 50x330 ‘Supershot’. However, the Super 40 and the 50mm Supershot have not so far proceeded beyond the development stage: work on the former has been proceeding at a low level, while the latter has been stopped entirely. No doubt that situation would change if a large order were in prospect, and it is understood that GD-OTS have been galvanised into activity over the Super 40 by the prospect of the WFLIP order discussed below.
There is one Western programme, currently at the live-firing test stage, which offers an alternative approach to the LAFV armament problem of providing high performance within compact dimensions: the Franco-British 40mm CTWS (Cased Telescoped Weapon System) developed by CTA International, a joint project between Nexter (formerly GIAT) and British Aerospace. This uses very short, telescoped ammunition just 255mm long overall (the projectiles are entirely enclosed within the case) with a very high performance, approximately equal to that of the 40mm Bofors and the 50mm Supershot (all three cases having similar propellant capacities). The rim diameter of the CTA round is the same as that of the Bofors 40mm case, but the Bofors round is twice as long. The gun installation is also designed to minimise turret intrusion: the ammunition is fed in sideways (pushing out the fired case as it does so) then the chamber rotated in line with the barrel to fire. The feed is on the axis of the trunnions, so does not move as the gun is elevated. There are clearly some significant advantages here, although its competitors point out that the trunnion loading means that the gun is out of balance, and argue that barrel wear is higher and the ammunition more expensive. However, the higher cost of larger calibre ammunition, plus the smaller quantity which can be carried, is counteracted by the fact that fewer of them would need to be fired to achieve the same effect.
The photo below shows experimental ammunition next to service rounds, all to the same scale: first, the 30x173, then the short-cased 40x164 Super 40 HE and the 40x218 Super 40 APFSDS (both since replaced by a common 190-195mm case), next an experimental high-performance loading of the 35x228, then the 50x330 Supershot (and a sectioned example of the APFSDS loading) and finally the 40x255 CTWS (standing on its head!) and a sectioned 30mm Rarden APDS for comparison.
The next photos show the 40mm CTWS and its ammunition:
Warrior Fightability and Lethality Improvement Project (WFLIP)
The UK's Warrior Mechanised Infantry Combat Vehicle (MICV) is currently armed with the 30mm Rarden cannon in 30x170 calibre, as is the Scimitar Combat Vehicle Reconnaissance (Tracked) or CVRT. This gun led the field when first introduced in the 1970s but has since fallen behind, due partly to its slow rate of fire (exacerbated by its manual reloading, in 3-round clips) and partly because it is not stabilised, so the vehicle has to stop to fire accurately. Furthermore, various attempts over a long period to introduce APFSDS ammunition failed to meet requirements until very recently (when a modified version of the RWM projectile was chosen), so the gun has been limited to APDS. The MoD has therefore established a requirement for a new gun armament for LAFVs which will be stabilised and able to utilise both APFSDS and HEAB ammunition, as well as featuring the latest sensor and defensive aid suites. The first beneficiary will be the Warrior.
A couple of years ago the UK announced its intention of holding a competition for the gun element of the Warrior Fightability and Lethality Improvement Programme (WFLIP - formerly known as WLIP), with a calibre of at least 35mm being specified. However, in 2007 this was amend to allow 30mm guns to compete, and three of the four contenders chose to use ATK's 30mm Mk 44 (the marinised version of the Bushmaster II, which it has replaced in production), with a potential upgrade to the Super 40 calibre, as follows:
1. Lockheed Martin Insys (together with Rheinmetall Landsysteme), based on a modified version of the existing Warrior turret.
2. GD-OTS, offering a version of their MK46 turret designed for the USMC's Expeditionary Fighting Vehicle.
3. Selex, teamed with OTO Melara to offer their HITFIST turret.
The fourth contender was the 40mm CTWS, or 40CT for short (which is also being considered for future French Light AFV requirements). While the traditional manned turret is increasingly being challenged by remotely-operated overhead mountings, demonstrated by the new German Puma MICV fitted with a 30mm Mauser MK 30-2 cannon, the WFLIP contenders all have manned turrets.
Interestingly, the increasingly sprawling BAE empire could have offered two other alternatives: the CV9035 turret with the 35mm Bushmaster III (with a potential upgrade to 50mm Supershot) and the Bushmaster IV in 40x365R Bofors. However, the company decided not to propose these, but to put its full weight behind the 40mm CTWS.
It is intended that the successful WFLIP contender will subsequently be carried forward for use in the reconnaissance version of the FRES (Future Rapid Effect System) family. However, this is causing a clash in priorities: the main purpose of the Warrior's cannon is to provide HE fire in support of its dismounted infantry, so volume of fire is an important consideration. The Super 40, at 44mm diameter, is significantly slimmer than the 65mm diameter 40CT round, so a lot more ammo can be carried in the same volume. FRES Recce, on the other hand, will mainly use its cannon for combating enemy LAFVs, so AP performance is paramount. Here the 40CT has an advantage, as its much greater propellant capacity provides significantly more muzzle energy than the Super 40 (around 500,000 joules compared with c.340,000). The 40CT also fires a heavier HEAB shell (1,000g cf 680-725g).
The contenders are at different stages of development. the 40CT has already progressed to live crew trials with a turret mounted on a Warrior, although a modified turret design was first tested in September 2007. Lockmart carried out a few remote-controlled test shots towards the end of 2007, but then announced they would be revealing a new turret design in March 2008. GD-OTS' MK46 turret has been tested on the prototype EFV, but has reportedly experienced lots of problems, apparently with the ammo feed. OTO's HITFIST turret is an established production item, but not in the WFLIP configuration.
Latest news: it was announced in March 2008 that the 40mm CTWS had been selected as the gun to be used in WFLIP and FRES Recce, although not necessarily in the BAE turret: invitations to tender for the turret installation are being issued. Whether any of the other contenders will bother to challenge BAE for this remains unclear.