In development since 2018, the Kingfisher munition is a novel and low-cost solution for warships developed by BAE Systems to counter underwater threats, particularly proliferating UUVs. Here we look at this weapon in detail and consider its potential selection by the Royal Navy.
BackgroundKingfisher is a naval gun-launched modular carrier system. This allows a warship to use its medium calibre gun to fire a shell which ejects a carrier with an ASW payload that could include small depth charges, sonobuoys, small UUVs, data nodes, acoustic decoys, or hydrographic sensors. The project has been self-financed by BAES’ innovation fund but has involved input from the Defence Science and Technology Laboratory (DSTL) and RN the Maritime Capability (MARCAP) staff. Kingfisher has initially been developed to be fired from the 127mm Mk 45 Mod 4 gun made by BAES in the US, which will equip the Type 26 frigate.
The project began with looking at replacement options for the Mk 11 depth charge still in service with the RN, this relatively simple weapon is based on technology developed in the first world war. The latest Mk 11 Mod 3 version has 4mm steel outer case and a nose section designed to withstand entry into the water at high speed and is fitted with stabilising fins on the tail. The depth charge is retained for air-dropping against submarines in the rare event of them being detected or spotted at shallow or periscope depths. Expensive and sophisticated homing torpedos such as Sting Ray are not effective at very shallow depths and are not a good counter to small UUVs or swimmer delivery vehicles.
The carrier shell concept is not unique to naval guns and the development of Kingfisher is dependent upon ongoing work to develop this type of round for the British Army. This includes larger 155mm gun but the Army is also considering moving to 127mm calibre as part of the programme to replace its 105mm L118 Light Gun. There are arguments around the mobility versus power of bigger weapons but standardising on 127mm would improve the commonality of logistics with the RN and munition development paths. The Army has a requirement for carrier rounds that can dispense sub-munitions for illumination, multi-spectral obscurants (smoke), electronic jammers and even leaflets.
Depth chargeThe most promising, simple and affordable Kingfisher concept appears to be the Depth Charge (DC) payload. Anti-submarine mortars delivering depth charges to short-range date back to World War II but gun launching is a new concept, enabled by the accuracy of modern naval guns. The Kingfisher shell is fired from the Mk 45 gun, the position of the target is pre-programmed and once at the correct point, the small expulsion charge pushes out the payload carrier which then deploys its folding fins to control the angle of entry into the water. The submunition sinks and at the pre-set depth, a depth fuze activates the 3 kg of high explosive.
The DC version of Kingfisher has 3 potential main roles; to attack submarines, attack smaller targets such as UUVs or special forces craft, and counter incoming torpedos. A sonar contact may be fleeting and hard to verify but the gun can respond in seconds and prosecute a target detected within an approximately 30km radius of the ship. Even if not sinking the submarine, a pattern of charges deployed close by would deafen its sonars and put it on the defensive giving the frigate and the ships it may be escorting valuable time.
Although the helicopter will be the first line of defence and ideally attack submarines before they get within heavyweight torpedo range, Kingfisher provides an inner line of defence and an option if the helicopter cannot get airborne due to weather or being in maintenance. As its stands, there is no current plan for the RN to acquire ASROC – a missile- that can deliver ASW torpedoes, launched from the Mk41 VLS out to around 24km. There is also no plan to fit a Magazine Torpedo Launch System (MTLS) for last-ditch close-in defence against submarines. Procuring Kingfisher would go some way to help mitigate the Type 26’s total reliance on the helicopter to prosecute submarines.
Autonomous underwater craft that range in size from small hand-launched vehicles to mini-submarines are proliferating and present a new and difficult threat to counter. These vehicles may be employed in a variety of ways to gather intelligence, attack seabed infrastructure, lay mines or trail a task group. The development of anti-UUV UUVs may be part of the answer in future but will be challenging and expensive to develop. Less sophisticated solutions could be the answer. A pattern of multiple Kingfisher charges would be a cheap and effective way to disable UUVs if detected. As small targets, a direct hit may be hard to achieve but UUVs are generally not constructed to be as robust as a crewed submarine and lacking the ability to self-repair, the shockwave from a near-miss is likely to render them useless.
When operating in the littorals there may be a need for defence against special forces combat divers and swimmer delivery vehicles. The small charges delivered by Kingfisher are ideal to provide the outer defence for amphibious operations if nefarious underwater activity is detected.
Possibly the most important of all Kingfisher’s capabilities could be in the torpedo defence role. If an inbound torpedo is detected the RN’s primary defence is provided by the short-range Surface Ship Torpedo Defence system (SSTD) which uses a passive towed array sensor. On detecting a torpedo it advises the command of the best course and speed to evade and launches acoustic decoys. Modern torpedoes may be able to distinguish between the ship and a decoy and Kingfisher also can be used against torpedoes detected at much greater range. By rapidly dumping a pattern of explosives close to the torpedo, even if not destroyed, could disrupt its fire control solution, deafen its sonars or cut the wire used for guidance linking it to the submarine. Small depth charges may also be a better counter to wake-homing torpedos that are harder to decoy by acoustic means, although this capability could be limited by the minimum range of the gun. The US Navy has abandoned its attempt to develop ship-launched anti-torpedo torpedoes due to insurmountable technical challenges and Kingfisher could provide a much simpler underwater defence option.
BAES has developed a Resonant Acoustic Mixing (RAM) manufacturing process which maximises the effect of the explosive in a small volume. By mixing the chemicals used to make the energetics using sound waves instead of mixing blades, explosive energy can be increased by up to 20%. RAM allows more viscous liquids to be used in the mixture and removes the need for solvents used to facilitate mixing blade movement. The explosive mixture is therefore more concentrated and powerful. RAM would be used in the production of the Kingfisher depth charge round and the New Generation Depth Charge intended to replace the Mk 11.
In surface actions, a flexible ladder of escalation can be used before opening fire; hailing by radio, illumination by fire-control radar, aggressive positioning or a warning shot across the bows. In undersea warfare there a very few options to discourage or deter an adversary without sinking them. Sending a burst of active sonar reveals the position of the emitter and may involve sacrificing the tactical advantage. Kingfisher offers a scaleable response to warn an adversary by laying small depth charges close by without sinking the target. As the line between war and conflict becomes increasingly blurred, having non-lethal response options assumes greater importance.
Other payloadsBAES say they have not begun development work but have other payloads for the Kingfisher round under consideration. Anything that is fired from a gun has to be engineered to survive forces of several thousand G during the extreme acceleration between the moment the propellant charge is detonated and when the round leaves the barrel. BAES/Bofors have some experience in engineering sophisticated electronic fusing for advanced shell types from the successful development of 3P ammunition. The small size of the carrier shell (approx 400mm long x 85mm diameter) obviously limits the physical size of these expendable payloads and they would necessarily have small batteries and a very short useful life.
Standard sonobuoys have delicate parts and would need to be made robust as well as miniaturised to fit. If these challenges can be overcome, the ability to rapidly deploy multi-static sonobuoys from the ship would be very useful. The data from the sensors could be combined with the ship’s sonar, helicopter dipping sonar or sonobuoys laid by other platforms to enhance detection range and accuracy.
If it is possible to build a very small UAV that can fit inside the shell, survive the launch stresses and deploy successfully this would be another useful tool. A visual picture of a target of interest up to 30 Km away could be relayed back to the ship within seconds from a gun-launched UAV.
There is also the potential for a specialised hydrographic sensor that could sample temperature and salinity in the water column as it sinks. After a reaching a preset depth it would release a transmitter that floats to the surface relaying the data back to the ship. Knowledge of the temperature and salinity layers in the ocean is important in understanding the performance of sonar.
Finally, Kingfisher could be used to deploy a floating data node. Similar to sonobuoys but designed to receive underwater data transmissions, these nodes could act as a communications relay with UUVs or a submarine operating in support of the ship. It is difficult to send high bandwidth data over long distances underwater and relay nodes could allow UUVs to communicate back to the ship or other platforms by satellite or radio data link.
Overall it is hard to make a case against adopting low-cost, low-risk Kingfisher, especially the depth charge variant. Let us hope that development proceeds quickly and is purchased in time to to enter service with the first Type 26 frigate in 2028.