A Blast from the Past: Medium-calibre Naval Guns for Defence against Drone Attacks
By: Joseph Kristanto, Benedicta Nathania Palit
Originally published in RSIS Commentary (Nanyang Technological University).
KEY TAKEAWAYS
The proliferation of low-cost drones is exposing the limits of today’s missile-centric naval air defence architecture.
Modern medium-calibre naval guns provide an affordable engagement layer against mass low-cost drone attacks.
Upgrading existing naval gun systems may offer a more practical solution for most navies.
COMMENTARY
Recent conflicts in Ukraine and the Middle East have marked the first time since the Falklands War that fleets have had to defend themselves against sustained aerial attacks. However, unlike previous conflicts, many of today’s attacks are carried out using large numbers of cheap, expendable one-way attack (OWA) drones.
From the Black Sea to the Red Sea, these systems have been employed to overwhelm a surface ship’s defences through sheer numbers while also imposing disproportionately high costs on the defender. Although current naval air defences have thus far proven tactically successful, such exchanges become increasingly difficult to sustain during prolonged periods of combat – and that is before accounting for the rapid depletion of onboard anti-air munition stocks.
For advanced navies with larger budgets and resources, the long-term solution is expected to take the form of directed-energy weapons. Yet such technologies are expensive and still not fully developed. For most other navies, waiting for these capabilities to mature is simply not an option. The more immediate challenge is finding affordable ways to improve their existing surface combatants’ survivability against the increasingly prevalent threats from drone attacks. Ironically, the solution may not require revolutionary technologies at all.
A Layered Defence Built for a Different Threat
Modern surface combatants are hardly defenceless against aerial threats. Most contemporary frigates and destroyers already employ sophisticated layered air defence systems consisting of long-range, medium-range and short-range interceptors, as well as close-in weapons systems (CIWS), to protect themselves and the fleet, or those vessels assigned to their protection, from enemy attack.
Such systems were designed to intercept high-end threats, such as long-range bombers and anti-ship missiles, as far away from the fleet as possible, and they continue to perform that role effectively today. One need look no further than the success of such systems in shooting down anti-ship cruise missiles and ballistic missiles in recent engagements in the Red Sea and Eastern Mediterranean.
However, the challenge arises when the very same systems designed to deal with these high-end threats are routinely deployed against cheap, attritable OWA drones. While they can defeat OWA drones easily – as demonstrated by the success of Western navies in downing numerous drones deployed by Yemen’s Houthi militants – doing so often requires expending missiles that cost many times more than the targets they destroy. While tactically successful, such counterattacks result in an unfavourable economic exchange, allowing the attacker to impose disproportionate costs on the defender.
Moreover, the number of missile interceptors carried onboard is finite. Modern warships may carry dozens of surface-to-air missiles, but prolonged drone attacks can drain those stocks. Every sophisticated interceptor launched against drone attacks is one less missile available to defend the fleet against higher-end threats such as hypersonic missiles and anti-ship ballistic missiles.
Advanced navies have turned to directed-energy weapons to combat low-end, high-volume threats. High-energy lasers are virtually inexhaustible and promise to defeat drones at a fraction of the cost of conventional missile interceptors. Yet these technologies remain expensive and technically demanding, preventing it from seeing widespread deployment – the Royal Navy being the only outlier in this regard.
Renewed Relevance of Medium-calibre Naval Guns
Although the technology itself is new, the operational challenge posed by the proliferation of low-cost OWA drones is not. Allied navies in the later stages of the Pacific War faced mass kamikaze attacks that sought to overwhelm fleet air defences through sheer numbers. Against this threat, medium-calibre naval guns, such as the 5-inch/38-calibre gun and the rapid-firing 40mm Bofors gun, played a critical role in defending fleets by providing sustained, dense defensive fire against numerous incoming aircraft.
While today’s OWA drones differ fundamentally from manned suicide aircraft, they create a remarkably similar operational dilemma: large numbers of relatively inexpensive systems that could overwhelm fleet defences. The challenge, therefore, is not simply to destroy these threats, but to do so efficiently and effectively without exhausting the ship’s limited air defence missile magazines.
This is where the descendants of World War 2-era medium-calibre naval guns deserve renewed attention. Today’s medium-calibre naval guns have evolved into advanced weapon systems. These guns are increasingly suited for engaging aerial and surface threats that would otherwise drain finite stocks of sophisticated interceptors. Systems including the Bofors 40mm Mk4, Bofors 57mm Mk 3 and Leonardo 76/62 – in Super Rapid, Strales or Sovraponte mounts – now offer capabilities that extend well beyond those of their predecessors.
Programmable and guided munitions further expand the utility and effectiveness of these guns. Leonardo’s DART projectile, for instance, is designed to engage highly manoeuvrable targets, including drones and anti-ship cruise missiles, with a higher hit probability than conventional ammunition. Similarly, BAE Systems’ Bofors 3P programmable ammunition allows a single family of 40mm and 57mm rounds to engage various targets through selectable fuse modes, improving flexibility during rapidly evolving engagements.
Compared to missile interceptors, these guns offer lower cost per engagement while allowing for larger magazines to enable repeated engagements during prolonged OWA drone saturation attacks without depleting a ship’s missile stock. Their increased engagement range compared with traditional CIWS also provides commanders with additional opportunities to intercept incoming threats before they reach a ship.
These developments are relevant across all navies; however, their strategic value is more critical for small and medium navies that cannot rely on a large inventory of sophisticated air defence systems. As demonstrated by the French and Italian navies’ success in shooting down enemy drones in the Red Sea, medium-calibre naval guns can become a practical means of fortifying layered defence systems through an affordable and readily available technology – one that is already mounted on many naval vessels yet has not been fully optimised to counter this type of threat. The challenge, therefore, is to adapt or supplement existing guns to play a greater role against these threats.
This growing recognition of the value of medium-calibre naval guns is reflected in contemporary warship development and procurement. The Royal Navy’s Type 31 frigates, for example, will be equipped with a 57mm Bofors Mk3 main gun and a pair of 40mm Bofors Mk4 secondary guns, allowing them to quickly throw a dense barrage of shells around a ship. Meanwhile, modern medium-calibre naval guns continue to feature prominently aboard new surface combatants entering service across Europe.
However, retrofitting additional medium-calibre naval gun mounts onto existing ships may prove challenging, particularly when the original hull was not designed to accommodate the extra weight and ammunition-handling requirements of these mounts. This is especially true with deck-penetrating mounts, which require more structural modifications and dedicated below-deck magazines. Meanwhile, non-deck-penetrating mounts may be easier to integrate, but they limit the number of shells available to the turret’s shell capacity. These trade-offs mean that additional gun mounts may be better incorporated in future ship designs, while existing ships could instead benefit from improvements to their existing gun systems, as demonstrated by the Republic of Singapore Navy’s plan to upgrade its existing medium-calibre gun mounts to the Strales 76mm guns.
Ultimately, contemporary naval warfare challenges are not only about firepower but also about ensuring that every layer of a ship’s defensive architecture remains operationally and economically sustainable. Rather than replacing anti-air missiles completely, medium-calibre naval guns restore an intermediate, affordable engagement layer that bridges the gap between highly capable yet costly long-range interceptors and last-ditch CIWS. For many small and medium-sized navies, strengthening this missing layer may be the most practical response to the rise of OWA drones.
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About Authors
Joseph Kristanto is a Research Analyst with the Maritime Security Programme, S. Rajaratnam School of International Studies (RSIS). Benedicta Nathania Palit is a Research Analyst at Indo-Pacific Strategic Intelligence, a Jakarta-based defence think tank.
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