Anthony G Williams

(This article was first published in Warship World magazine in the summer of 1989. The Cold War was still at deep freeze level, and tactical nuclear weapons were in every major power's arsenal. Some of the points made here have since been overtaken by events, but the thrust of the argument is still valid)

The Summer 1988 edition of Warship World contained a small item of information whose significance might have passed unnoticed. It was reported that Vickers, FMC and Oto Melara were co-operating to design a tri-national 155mm naval gun intended for the NFR9O, the proposed standard NATO frigate for the next generation of warships.

On the face of it this appears to be no more than a logical standardisation with NATO's main artillery calibre, with the heavier shell giving a useful bonus for shore bombardment, but it appears curiously at odds with the recent trend to smaller calibres with high rates of fire in order to combat attacks from aircraft, missiles and fast patrol boats. For example, the USN Oliver Hazard Perry class frigates were designed with a 76 mm gun and the new Canadian Patrol Frigate is intended to use the 57 mm Bofors as its main gun armament. Even more drastically, later versions of the RN's new Type 23 frigate will not be fitted with the 4.5 in gun and will therefore be relying on armament of no more than 30 mm calibre (plans which did not, of course, happen).

The significance of the proposed 155 mm gun almost certainly lies in a number of lines of recent technical development which could well be brought together in the near future to restore the big gun to a more prominent role in naval armament.

The Decline of the Anti-Ship Missile?

This might appear to be a provocative headline, but the simple fact is that the current pre-eminence of the anti-ship missile is under increasing threat. Defences in the form of decoys, quick-reaction AA missiles and radar directed rapid fire close-in weapon systems of 20 to 40 mm calibre are increasingly being fitted to major warships. It is arguable just how effective these will be in battle but they should certainly account for a fair proportion of attacking missiles.

This will cause serious problems for attacking warships since, because of size, weight and cost constraints, most ships only carry four to eight anti-ship missiles. It is highly probable, therefore, that in a future action of any magnitude ships, having fired off their missiles, wilI find themselves with an enemy still to fight and only one or two guns to fight with. The same could also apply, albeit to a lesser extent, to anti-aircraft missiles. It is presumably for this reason that the USSR has developed the formidable new high velocity rapid fire 130 mm gun first fitted to the Sovremennyy' class destroyers.

New Ammunition Developments

Positive steps leading to the possible resurgence of the big gun are all concerned with sophisticated new ammunition developments involving advanced guidance and control systems and measures to increase range.

The first guided shell in service is the US Army's Copperhead, which can be fired from standard 155 mm artillery and homes in on any target which is being illuminated by a laser of the appropriate type. An equivalent naval version for the USN's 5 in gun has also been developed. The benefit of such ammunition for precision shore bombardment is obvious, with laser-equipped naval gunfire support forward observers put ashore in advance to illuminate pinpoint targets. However, the need to keep a laser accurately pointing at the target greatly reduces the potential of this system for anti-aircraft and especially anti-ship purposes.

The French Navy has been working on infra-red homing projectiles for its 100 mm gun, but lR is an unreliable guidance method in poor weather. A better choice is millimetre-wave radar, which is more reliable, sturdier and cheaper. An early application is Marconi's Merlin; a homing anti-tank round which can be fired from a standard 81 mm mortar (since cancelled). A system capable of picking out a tank from above should have few difficulties in coping with naval requirements.

Steering guided shells towards the target has caused some problems. Copperhead has extending fins which use up a lot of space in the body and therefore lead to a very large and cumbersome projectile. Rocket assisted shells, which have been in existence for many years in unguided form, could be steered by means of jetevators which deflect the rocket efflux. The most interesting possibility for unpowered shells has been developed by Raytheon and consists of lines of tiny explosive charges along the body of a conventional looking shell, which are triggered as required to alter the flightpath of the projectile. This system has been demonstrated successfully with shells of only 40 mm calibre. Finally, the range of 155 mm artillery shells has been increased sharply by the introduction of ERFBBB (extended range full bore base bleed) ammunition. This is a large-capacity shell of excellent aerodynamic form which contains a small quantity of combustible material in the tail, not to act as a rocket but to smooth the airflow behind the shell. When fired from 45-calibre artillery this projectile ranges to over 21 nautical miles; slightly further than the USS Iowa's formidable 16 in guns can reach and over 9 nm further than the RN's current 4.5 in gun.

Prospects for the Future

Sooner or later it is likely that all of the developments described above will be brought together to create long range homing ammunition which will transform the importance of the naval gun. Anti-aircraft shells might have rocket assistance, to be ignited as soon as the target is detected by the shell's sensor. Anti-ship missiles would carry a heavier explosive charge instead. The advantage of using the standard 155 mm calibre is obvious in terms of both spreading development costs and achieving greater destructive power per shell in order to justify the cost of the guidance and control systems. Also in existence are 155 mm nuclear projectiles, which apart from other uses would make highly effective long-range depth charges for use against enemy ballistic missile submarines. A single-barrel automatic naval gun mount, capable of 15-20 rpm, would probably weigh around 50 tons; about the same as the twin 4.5 in mounting fitted originally to the Leander class frigates. With a 55 calibre barrel a range of at least 24 nm could be expected, about the same as Exocet MM38 fitted to many of our warships.

Weighing up the Advantages

What would be the advantages over existing missile systems? These can be summed up as volume of fire, rate of fire and cost. It is obvious that provision could easily be made for each ship to carry several hundreds of rounds of ammunition, which with modern mechanical shell-handling techniques could be fired at a rapid rate.

More importantly, as each shell would have its own self-contained homing system it would not need to be steered on to the target by ship -mounted systems, merely fired on a ballistic course which would be followed until the target was detected. The rate of engagement of fresh targets would therefore only be limited by the ability of the ship's fire control system to re-aim the gun after each shot. This has obvious advantages when dealing with large numbers of attacking aircraft or missiles. In the anti-ship role the shells would clearly be more difficult to destroy than conventional ASMs, particularly as several could be fired in rapid succession at each target.

The cost saving would be in two areas; after the initial development costs, the production of this type of ammunition should be relatively cheap, and the warship itself would not need any special guidance systems or related equipment other than a fire control radar and ballistic computer.

The successor to the Type 23 frigate might therefore have much simpler and cheaper weapon systems with a main armament (apart from its helicopter) of one 155 mm gun, 
probably backed up by a 30 mm CIWS for last-ditch defence. While losing the very long range of the Type 23's
Harpoon anti-ship missiles (which may not in any case be
very practical because of targeting problems), such a ship would be far better
equipped to cope with an extended naval action, with 'raids' by large numbers of aircraft or
missiles and of course with shore bombardment tasks.
It should also be considerably cheaper.

(Postscript: if such developments were to occur, it is interesting to speculate on the implications for warship design. If taking hits from guided
shells became unavoidable,
then armour protection for vital systems would be an obvious response. This would tend to push up ship size. It
would also put an upward pressure on gun calibre in order
to defeat the armour and damage the larger ships, which in turn would increase
armour thickness and so on. Now what did we do with those battleships?)