The pitfall of surface marine drones. Technical and tactical considerations

(To Marco Bandioli)

The insidious threat represented by marine drones as a surface attack weapon against "naval units" (i.e. warships) requires the evaluation of different factors that contribute to providing a more detailed picture of the issue. Since the topics addressed are extremely vast and complex, it is necessary to address the topics in fairly general terms without giving up some technical details which will be essential for a full understanding of the subsequent technical-tactical considerations.

Marine drones, compared to aerial or terrestrial ones, can represent a rather difficult target to identify due to the fact that technology, for now, is not yet able to fully address some limits that the nature of the sea imposes... except with the synergistic competition of multiple high-tech devices.

From a doctrinal point of view, drones are generally defined with the military-technical acronym of "UV" (Unmanned Vehicle – vehicle without human presence on board) and, in particular, are further classified with the addition of letters which serve to immediately identify the physical element (sky, earth and sea) in which they are intended to operate. The drones that operate at sea, the so-called "marine drones" (also called "naval drones" or "drone boat" or "sea drone"), have always been classified with the acronym UV, but in this case the "V" rather than "Vehicle" it is often and rightly understood as "Vessel" (i.e. as a ship or boat). The acronym UV (Unmanned Vessel) has however fallen into disuse as marine drones are directly divided in relation to the physical environment in which they are used, i.e. whether they operate "above" or "below" the surface of the sea:

  • marine life above the sea surface, or “surface” UPS (SUV and ASV) - USV (Unmanned Surface Vehicle) - divided in SUV (Surface Unmanned Vehicle), if driven remotely by a human operator (via radio control, remote control or satellite), and ASV (Autonomous Surface Vehicle), if the driving is totally autonomous (via artificial intelligence, programming or via satellite);
  • marine life beneath the surface of the sea, or “underwater” (AUV/UUV and ROV/ROUV) - AUV/UUV (Autonomous Underwater Vehicle / Unmanned Underwater Vehicle) if the driving is completely autonomous (via programming or artificial intelligence units) and ROV/ROUV (Remotely Operated Underwater Vehicle) if any form of guidewire is used.

The missions they can carry out are multiple and can vary from surveillance to armed patrol, from reconnaissance and intelligence activities to pure attack actions against enemy military shipping.

In the conflicts that have emerged recently, surface marine drones have been used both by regular armed forces (e.g. the Ukrainians) and by terrorist groups (e.g. the Yemeni Houthis), however using them as "explosive drones" exploiting an idea which the Royal Navy, first of all, had already developed during the Second World War with the creation of different types of "assault motorboats" called "explosive boats" (armed either with 2 kg of explosives or with torpedoes or with bombs) and led by a pilot who, about 300 meters from the impact with the enemy ship, was thrown into the water (photo).

A particular species of marine drones are therefore used solely as a weapon carrier to hit and sink ships or, at least, to significantly damage them.

The sinking or damage of a ship depends on many factors such as the type and size of the target ship, the number of drones used for the attack, the quantity and type of explosive with a high disruptive effect, the type of trigger used as well as the point or points where the ship must be hit.

For completeness of information, if the marine drone carries an explosive device that has not been manufactured industrially but in an artisanal way, even partially, the drone takes on the term "WBIED" (Water-Borne Improvised Explosive Device) or “Improvised explosive device transported by sea/water”.

The small boats that are currently used as marine drones have different versions but can be configured, in general terms, according to the following main characteristics: they have a hull that resembles a canoe or a kayak with propulsion guaranteed by one or two 200/300cc engines. 3 hp, a very low profile shape with superstructures that on average do not exceed one meter above sea level, little draft, a length that can range from 15 to 150 meters, they can carry from 350 to 4 kg of explosives (or a system 50-cell rocket launcher), can reach speeds even higher than 400 knots and can have an operational range of more than 800 nautical miles (≈ XNUMX km).

Thanks to a camera installed on the drone, in "first person" viewing mode, the operator who remotely pilots the drone is able to both verify (recognize) the identity of the target to be hit and change the speed, the course and angle of attack, in relation to the state of the sea and the position, orientation and speed of the target.

It is clear that this type of threat places the "Naval doctrine of surface warfare" having to deal with a substantially asymmetric and unconventional dimension of the issue, both due to the disparity in the armaments used, the tactical methods used and the related disparity of costs and necessary financial resources.

It is now necessary to highlight that the operational procedure according to which a target is searched for and then destroyed is divided into two sequential processes.

The first is called “Target Acquisition” and is developed in 6 phases: Research actual (if there is the presence of a target), discovery (the presence of a target is determined), location (the geographical position of the target is determined), recognition (the generic nature of the target is determined; e.g. aerial target), identification (the specific nature is determined; e.g. enemy anti-ship missile) e tracking (the "track of the target" is continuously followed through a specific radar, and various equipment, determining the electronic parameters to then carry out the so-called "tracking" by a shooting radar, to which the already prepared weapons are subservient fire for action).

The second process is called “Target Engagement” which responds to the specific "Rules of Engagement" envisaged for the mission. The engagement can be of the type “direct", if it is developed on the discovery distance of its sensors, or of type "planned”, if it is developed on target data received via tactical links from other units.

The engagement also includes two phases: thefire action (with the use of the most suitable weapon system depending on the nature, speed and distance of the target) and the destruction of the target itself (continuous fire action until the target is shot down, sunk or destroyed).

Therefore, the greater the distance at which a target is discovered, the greater the time available to develop the acquisition and engagement process: however, in unfavorable tactical situations the total time available could be reduced to a few minutes... if not to a handful of seconds (keeping in mind that an attack could be carried out not by a single isolated drone but by a group of drones coordinated with each other).

This is not the opportunity to delve into the technological complexities of radar systems or their technical details, but it is worth remembering that radar (substantivization of the acronym RADAR = RAdio Detection And Ranging) is an electronic device that allows the detection and tracking of a target of which it provides, in its simplest configuration, the distance, bearing and speed. Its operating principle is based on the transmission of energy in the form of radio waves which start from an antenna, reach a possible target from which they are partially reflected and return to their radar source as if they were an echo: it is for this reason that the “raw figure” of the target that appears on the radar screen is called a “radar echo”. This radar echo can be "processed" electronically by a radar operator and a synthetic trace is "hooked" to the raw echo which, based on a specific symbology, a color and a code, visually provides a certain amount of further information on the nature and identity of the target (bearing, distance, course, speed, altitude, air signature, surface signature, unknown signature, friendly signature, assumed hostile signature, enemy signature).

The classic display of the radar action takes place on a circular screen which is called "PPI" (Plan Position Indicator) and is a representation in which the ship is at the center of the screen with the display of the exploring sweep of the continuously rotating radar beam at 360 degrees around the ship itself.

A radar representation can however also work beyond radar detection range, taking the scale beyond the nominal range, thanks to "dialogue links between radar systems" carried out with particular tactical communication systems (called TDL -Tactical Data Link): in this way it is possible to see and enhance the synthetic traces of very distant targets sent by other ships, planes, helicopters or land stations that are part of the same preventive warning device, of "initial alarm" (the so-called EW- Early Warning).

Radars have different classification criteria, but the one used in the military field is the one that takes into consideration the ranges of radio and microwave frequencies that are used by specific radars, thus establishing "frequency bands" whose denomination identifies the use of the radars themselves (e.g. "Sierra" band: surface discovery radar; "Xray" band: shooting radar; "Lima" band: multifunctional radar).

On board a naval unit, armed with artillery and missiles, there are on average 5 types of radar: radar by navigation, radar of surface discovery, radar of aerial discovery, radar of tiro and radar missile guide.

However, there are now "multifunction radars" (photo) that they manage to combine multiple radar functions into a single system.

In any case, the propagation of the energy emitted by the various radars, also depending on their frequency and the type of pulses used, is subject to various interferences which can be grouped into two types: purely environmental interference ed electromagnetic interference generated by enemy electronic systems. However, it is in particular an environmental interference that confuses a surface detection radar and therefore makes the attack of a marine drone treacherous.

Returning to interference generated by the enemy, in the doctrinal context of "Electronic Warfare" the "electronic" attack on radars is defined as "Jamming" (disturbance) and is carried out using electronic equipment and devices that disturb (creating strong signals that affect both communications and transmissions ), to deceive (creating false "echoes") or to saturate (creating background electronic "noise") the electronic equipment.

Previously, electronic attack and defense activities had different and more complex definitions but, in the current historical-technological moment, it is sufficient to say that the various forms of "electronic counterattack", implemented to counter every form of Jamming enemy, is entirely devoted to the development of defensive technology of radar system software.

Interference instead environmental that affect the capabilities of the radar are the effects of some physical phenomena that affect electromagnetic propagation: thedispersion” of electromagnetic radiation due to the deflection of the waves, i.e. they change trajectory, the “refraction” of the waves due to the non-homogeneity of the atmosphere, the “attenuation” due to the various gases present in the atmosphere, the “diffraction” due to the curvature of the earth and the “reflection” of energy when the wave encounters a target and some of its energy is reflected back to the radar. This "reflection", this quantity of reflected energy depends on the size, shape and composition of the target...unfortunately, however, this reflection also occurs from substantially "unwanted" targets, such as rain, snow, birds or other bulky and which therefore create "confusion" to the radar, and to the consequent video representation.

In technical terms this phenomenon is called "Clutter" (confusion), which can be defined as “any unwanted radar echoes that cause confusion” and it can represent a big problem as it can hide small radar echoes from radar detection, such as surface marine drones.

From a tactical point of view, the marine environment is more complex than airspace and, even if the speeds involved are different, identifying an approaching aerial target (missile, rocket, aircraft or drone) in time is paradoxically easier also in consideration of the fact that the airspace is, technologically speaking, more uniform and "transparent".

In reality there are different types of clutter (distributed, concentrated, surface, volume), but what interests you you can call it "sea ​​clutter” (photo), that is clutter which appears on the radar when the surface of the sea, no longer completely calm but with small low and short waves, begins to create many unwanted echoes which "dirty" the radar representation in which it is then really difficult to identify a substantially immersed target between fictitious targets or follow one already discovered and tracked, keeping in mind that in such circumstances even a "synthetic trace" could "detach" from the raw reference echo and proceed on fake data.

This situation can make the attack of an enemy surface drone (perhaps even built with "stealth" materials that reduce its electromagnetic signature) particularly insidious since the wave motion of the sea, naturally within those limits that can allow the drone to be navigation that maintaining a route can hide its rapid approach from the radar itself without its presence being perceived in time or, even worse, the attack already underway.

Under certain unfavorable conditions, the clutter can preclude surface radar detection in a sea area around the ship that can extend up to 5 nautical miles (≈ 10 km). In general terms, in optimal visibility conditions, a marine drone, assuming an average height of one meter on the sea surface, can be optically identified at a distance of 9 nautical miles (≈ 17 km) considering the surveillance personnel positioned approximately at the generic height of 12 m. on the surface of the sea (e.g. the bridge): this "optical range", understood as the possibility of "optical discovery", therefore exceeds the critical area of clutter.

In light of what has been said, the problem of clutter can be partially (sometimes totally) overcome, with the use of "Opto-electronic discovery systems", both infrared and light intensified, thus allowing a high probability of discovery even in the middle of the night and/or in meteorological conditions adverse events (see video "DSS-IRST: the acronym for Naval Security in the Military sector")

In any case, a marine drone loaded with explosives must necessarily be neutralized before it impacts the side of the ship and possibly at a "conservative" (precautionary) distance from the ship of no less than 500 meters as an explosion even just in the vicinity of a ship can cause damage not only due to the force of the shock wave produced by the explosion but also due to the projection over a considerable distance of those fragments ("splinter effect") deriving from the destruction of everything existing around the explosive (the casing of the explosive explosive, engine and hull of the drone, equipment, as well as any metal elements specially inserted into the explosive).

Keep in mind that splinters arriving on the superstructures of a naval unit can also cause serious damage to the ship's equipment and sensors, making it, electronically speaking, "blind, deaf and dumb". Considering now that...

► the range of a surface discovery radar in an optimal propagation situation can even reach 100 nautical miles (≈ 190 km),

► the range is however quite variable depending on the geographical area of ​​the planet you are in,

► the possible assistance of helicopters or drones in flight that can remotely confirm the identity of the target may be missing,

► the weather and sea situation may not be optimal,

it can reasonably be assumed that the defense of the ship against a marine drone can be carried out by essentially considering three defensive levels: starting from a distance of approximately 10 nautical miles (≈ 19 km), distance understood, for on-board artillery, as "medium range defense", then moving on to a "short-range defense", from a distance of approximately 5 nautical miles (≈ 10 km), ending at "point defense", i.e. a "close" defense that takes place below the nautical mile (≈ 2 km) from the ship.

The fight against the threat is therefore carried out with naval artillery systems, of different calibre, with a high rate of fire and with the possibility for the guns to use both conventional ammunition and guided ammunition (with greater range and equipped with precision guidance systems). .

For short-medium range engagement, guns with an average caliber of 76 mm are used, while for short range engagement, both machine guns and automatic cannons are used (i.e. a modernized version of a remote-controlled machine gun with a mechanism automatic reloading, without the need for a servant) which present different types of caliber which can range from 20 mm. to 40 mm..

As far as "point defense" is concerned, heavy machine guns (12.7x99 mm cal.), grenade launchers or shoulder-mounted rocket launchers are always good: it seems that groups of contractor for this purpose, seafarers also take on board grenade launcher machine guns (AGL Automatic Grenade Launcher) in cal. 40 mm. to increase defensive positions.

Definitely, identifying a surface drone and sinking it is not easy but the contribution of multiple surveillance and "alert" systems they can make a difference, as well as, "in extremis", the ship's ability to maneuver and increase speed... just as if it had to avoid a torpedo!

Photo: web / X / US Navy / Online Defense