Introduction
The Russia-Ukraine conflict is a grim reminder of an ironic reality of warfare, ‘The more it changes, the more it remains the same’. Who would have thought in February of 2022 that Russia’s swift, short special operations in Ukraine would last for two years and, after a while, stagnate into a battle of firepower? The advocates of reducing traditional artillery from the armed forces inventory need a second thought. Yet, in the last decade, the ‘Artillery Gun’ has seen negligible change. Efforts to improve lethality and range have concentrated more on the ammunition than the gun. This article tries to understand the reasons for the stagnation and the future of artillery guns.
The artillery guns have stagnated at 155mm calibre. It’s been a while since any new calibre gun has entered the artillery family. For guns like the M110A2, the 203 mm (9.2 inches approx) gun of the US Army was not a step in climbing the ladder; it was a development in yesteryear. Like the German Rail Gun of World War I and II (14.5 inches and 30 inches approx.), it was an effort to invent something new to influence the immediate need rather than a long-term weapon system. The evolution of artillery guns has been a function of tactical need, metallurgy and technology. The proliferation of artillery calibres took off after World War II when the arms race caught pace. The Soviet bloc opted for the 122mm and 152mm calibre guns against the NATO block countries,which opted for the 105 mm and later the 155 mm calibres. Though tiny in millimetres, the difference is enormous in terms of philosophy. The two rival blocks intended to be different from each other and, as a strategy, ensured the opponents could not use the ammunition or the guns should they ever fall into their adversary’s hands.
155 mm, the Standard Calibre
The experience of World War II and the subsequent division of Europe necessitated unity in thought processes amongst the members of the NATO alliance to fight their rival block: the Warsaw Pact countries. The unity was in terms of fighting together the perceived enemy on the battlefields, which were mainly in Europe. Artillery was the first to lead this thought process. All guns were designed for a standard calibre with standard ammunition so they could be manufactured universally and used by all the NATO allies. Such a move ensured the rapid manufacture and movement of artillery guns and ammunition to ward off an intended threat anywhere across Western Europe. A similar thought process had run through the Warsaw Pact countries, too. Hence, while the NATO countries opted for 155 mm as a standard artillery calibre, the Soviets opted for 152mm. We will concentrate the discussion on 155 mm and not discuss the 152mm calibre, which has also met the same fate.
Why the fixation for 155 mm calibre? A possible reason was that a 155 mm diameter was the minimum required to propel a nuclear artillery shell should a need arise. The nuclear artillery shell programme which went into manufacture was; the US W58 155mm nuclear artillery shell. Apart from the above, theoretically, calibre and calibre length (Length of the Barrel) determine the gun’s weight, size, shape and weight of the ammunition. The efforts for future development aimed to reduce the artillery’s supply chain and increase its firepower. By the time the Gulf War II broke out, the ‘Operational Doctrines’ had rapidly changed; degradation of depth targets and concurrent attacks on objectives in front and depth were a norm. The new tactical doctrines required weapons which could provide intimate fire support and destruction at the same time. The new guns were able to deliver fire support to 40 km. Where the ranges to targets were greater than 40 kms, tubeless artillery with ranges from 70 to 140 km was employed. One of the principal requirements of Field Artillery is to provide close support to infantry and armour formations when contacting the enemy, whether in an ‘Attack’ or in ‘Advance’. This requirement alone puts heavy demands on the field artillery guns in terms of their design, ballistics, and training. It demands precision of the highest order—a provision no other weapon system can fulfil at the desired scales. Thus, artillery guns are the best instrument for last-mile fire support.
By the time, the 155 mm 39 calibre guns had made their way into the inventories of large armies like the Indian Army with the FH 77 B 155 mm Bofors guns, the military thinkers were demanding longer ranges. The simplest way was to increase the barrel lengths, technically described as calibre length. The 39-calibre length barrels gave way to 45 calibres, allowing a more extended range for a high explosive (HE) shell. The 45 calibre length gave way to 52 calibre length. That’s when the range for a HE stagnated at around 35-40 km. A longer barrel helps increase the range by allowing the propelling gasses to act on the shell base for longer time.
The designers were asking: Could artillery guns be designed to provide close support and fire in-depth well beyond 40 km? That depended on whether there was a need for an artillery gun to fire that deep. An artillery gun/ howitzer is an expensive and complex weapon system, especially modern guns, compared to tube (Rocket) artillery (Life Cycle Cost per unit). Hence, undertaking engagements of targets in depth by tube (Rocket) artillery was a more efficient option. Doing the same with field artillery guns would mean increasing the weight of the gun and ammunition system. The configuration of a 155mm gun had reached an optimum level, such that a slight increase in range would demand a considerable increase in size and weight. It’s the same analogy as improving the efficiency of a machine after it reaches its peak, e.g. 90%. Every incremental change would require far greater effort and resources. The table below would explain the above.
The table indicates that an increase in calibre does not necessarily increase range. It could deliver a higher explosive content to the target. Yet the rates of fire suggest that a 155mm can deliver a higher quantity of explosives on the target within one minute. This dichotomy is why the US Army discontinued using 203mm M 110 A2 in the early 1990s.
To understand the constraints of going in for higher calibre, a simple internal ballistic equation can prove the degree of difficulty involved. When moving from 105mm to 155 mm, as per simple calculations, the cross-sectional area of the shell will increase by 2.17 times approximately, indicating that, all else being equal, the larger shell could have more than twice the kinetic energy, giving it a potential for greater range. However, when the gun’s weight is considered, from 105 mm to 155 mm, the weight has increased by 4.38 times to 14 tons, while the range has increased by 3.5 times. It is possible to calculate hereafter for every increase in 10 mm calibre how the weight of the gun will increase.
As per calculation, every 10 mm increase in calibre could lead to an increase of 2. 16 tons in weight and 6 km in range of the gun on a linear basis. In reality it will be substantially less due to the phenomenon of a diminishing rate of returns. This mathematical explanation is an elementary representation of a complex interplay of factors such as the increasing rate of diminishing returns, the change in ammunition weight and propellant charge and the resultant recoil gasses and internal chamber and barrel pressure. All of these would increase the gun’s weight. Similar equations will play out for an increase in the weight of the ammunition. Thus, an increase in range and lethality would get into a steep upward-moving marginal utility curve along the Y axis, representing weight, where the graph line will climb exponentially due to increase in the calibre (represented on X axis) of the gun more than the present 155mm. In summary, an increase in calibre would lead to a substantial increase in weight, and thus be inefficient.
The above argument is made for increasing the calibre of the bore, meaning increasing its diameter. It was self-evident that it would be counterproductive. Yet some believed that instead, keep increasing the calibre length (Barrel Length), keeping the calibre of the boring standard, say, at 155mm. After the 52 calibre length, an attempt was made to increase the length beyond 52. The US Army attempted a prototype development with a Program called the M1299 Extended Range Cannon Artillery (ERCA). This program envisaged a 155 mm gun with 58 Calibre length mounted on an M109 Paladin PIM (Paladin Integrated Management) armoured howitzer chassis to achieve ranges over 40 km. The gun fired and may have achieved higher ranges, but the wear and tear on the barrel was enormous, jeopardising the safety. At the end of 2023, the ERCA Program remains undelivered to the US Army despite its deadline having expired.
Way Forward
Given the futility of increasing the calibre or calibre lengths, developments in artillery, if any, would not be in the gun/howitzer family but in Hypervelocity or laser guns, which would be a new stream. The way forward for field artilleries worldwide, including India, is to improve ammunition performance and types. Newer types of ammunition, like the RAP, base bleed or the stabilised fins or nubs on the shell body, have already improved the aerodynamic performance. The same could be revisited. Improved metallurgy could lead to a higher threshold for sustaining pressure inside the barrel. It could also pave the way for more optimum utilisation of propellant gasses; thus, increasing artillery rounds’ range, lethality, and precision.
Conclusion
Artillery guns have stabilised at an optimum calibre of 155mm and calibre lengths of 52 calibres and below, like 45 calibres and 39 calibres. For the reason explained in the article of diminishing returns between the increases in calibre leading to less efficient results, the chances that a newer calibre standard artillery gun will emerge on the horizon very soon is doubtful. The demands of current tactical doctrines and the proliferation of longrange multi-barrel tube artillery preclude any further design development in the gun-howitzer family. Indian Artillery has invested in the 155 mm 52 calibre Dhanush Gun produced by the OFB (Ordinance Factory Board) as its gun for the future. The chances that a desire for a newer calibre would drive any further developments in artillery in India or abroad are very slim.
