Stealth Warships

We lift the lid on the latest covert vessels that are taking the art of sneaking to a whole new level.

Stealth relies on five core principles when it comes to military vessels: materials, coatings, geometry, noise and tactics. While the latter is situation dependent, the first four are physical qualities that can be modified to enhance stealth with advanced technologies.

Materials are based on composites such as fibreglass rather than hard metals and the incorporation of negativeindex metamaterials (NIMs). These latter artificial substances are designed to be all-but invisible to specific radar frequencies. Some vessels are also being built with demagnetization belts – a process that involves encircling a ship with superconducting ceramic cables.

Covering a vessel with radar-absorbent coatings such as iron ball paint – tiny spheres of carbonyl iron or ferrite – can also reduce a radar cross-section. Coatings are referred to as RAMs (radar-absorbent materials) and work by transforming radar waves into heat energy. This process works as the carbonyl iron coating has an alternating magnetic field, which when hit by radar waves begins to oscillate at a molecular level, trapping the incoming signal within the material and dissipating its energy as heat.

Geometry is also crucial to remaining undetected. In terms of radar, complex structures offer a far crisper, easier-to-identify return image than those with a simple geometry. As such, modern stealth warships and submersibles are designed with this in mind, often installing protective domes over the mast and sensors, called radomes. Similarly, today’s vessels have incredibly clean and angled hulls with few doors and faceted hangars.

Noise in terms of maritime vessels can come courtesy of ship wake, heat generation and operating machinery. In fluid dynamics a wake is the area of disturbed liquid flow downstream of a ship. This wake can be detected by side-scanning synthetic aperture radars (SARs), which can then work out both the ship’s position and direction plus sonar installations.

To combat this, the latest stealth ships are generally outfitted with low-power diesel motors with specialised heat-dissipation systems to reduce their thermal signature. Active acoustic camouflage systems beneath the hull, meanwhile, can generate a constant series of small bubbles, effectively disrupting sonar images.

In this article We explores four examples of cutting-edge military vessels that have been designed with covertness at the top of the priority list, from out-and-out destroyers through to agile, wraith-like submarines.

What are masking systems?

Masking systems in marine vehicle applications work by reducing radiated noise generated by the vessel’s propulsion system and general movement. This is achieved by mounting machined perforations on the sides and propellers of the ship, through which compressed air is pumped at a high rate. This action creates a barrier of tiny air bubbles around the vessel and propellers that traps mechanical noise and disrupts sonar waves. The result of this is that enemy sonar installations, such as those found on military submarines, receive a heavily distorted image of the scanned area, with vessels commonly shrouded in a pattern akin to rain falling on the ocean surface.

The Infiltrator – Type 26 Global Combat Ship

Capable of delivering cruise missiles, combat helicopters, unmanned hunter-killer drones and a barracks load of Royal Marines into coastal warzones, the new Type 26 Global Combat Ship being built by BAE Systems is set to deliver a platform for unprecedented covert operations while at sea. Despite weighing about 5,400 tons and measuring a whopping 148 metres (486 feet) long (that’s one and a half times the size of Manchester United’s football pitch), the Type 26 appears merely as a small fishing boat on radar systems. This means that when it becomes operational in 2021, it will be able to traverse the globe without detection and infiltrate the most hostile areas. The fishing boat-sized radar cross-section comes courtesy of the sleek, low-profile hull, specially angled deck panels, multi-installation radomes and advanced anti-radar/sonar damping equipment. This tech will cloak on-board vertical missile silos, an array of medium-calibre guns and a huge hangar containing both Merlin and Wildcat helicopters.

The Crusader – USS San Antonio

The USS San Antonio amphibious transport dock excels in its ability to efficiently carry and covertly deliver military vehicles and ground troops. This would not be so impressive if it wasn’t for the size of the San Antonio, which weighs in at 25,000 tons – more than the Type 26 and USS Zumwalt combined!

So how is such a gargantuan vessel cloaked? Well, aside from the basics, it comes down to ship-wide attention to detail. Major antennas are mounted on platforms inside two advanced enclosed mast/sensor (AEM/S) systems rather than on yardarms. Deck edges are bounded by shaped bulwarks rather than lifeline stanchions; all exterior equipment is recessed or flush-mounted; bulky things like boat-handling cranes fold down when not in use; while the anchor and anchor hold are designed to minimise radar backscatter.

This strict adherence to stealth principles transforms the radar cross-section of what is essentially a small aircraft carrier into one under half its size. This allows it to sneakily approach target coastlines and launch air-cushioned landing crafts, amphibious assault vehicles, attack helicopters, military jeeps and even armoured personnel carriers onto land along with a maximum 699 soldiers.

The Annihilator – USS Zumwalt

The USS Zumwalt – the lead ship in the upcoming Zumwalt-class of destroyers – doubles down on the Type 26’s damage-dealing capabilities while maintaining a purist dedication to staying invisible. Stealth first. Features include an aluminium/glass-fibre composite structure, a wave-piercing hull that leaves almost no wake and an exhaust suppressor to reduce its infrared signature. On top of all this, a high-angle inward sloping exterior, noise reduction system and a trapezoidal, radome-inspired command and control centre make this near-15,000-ton titan nothing but a ghost on radar. This arsenal of stealth technology allows it to slip through the waves like a harpoon, ready to deploy an arsenal of a much more explosive nature on unsuspecting targets.

Interestingly, the Zumwalt even extends its stealth mantra to its weapons, with every gun, missile and torpedo launched by integrated computer systems. As such, far from crew members having to man gun emplacements on deck or load missiles into launchers manually -generating more noise – the Zumwalt allows the sleek, minimalist deck to remain undisturbed, so an offensive can be launched without compromising its location.

The Wraith – Virginia-class submarine

While the Type 26, USS Zumwalt and USS San Antonio are demonstrating advanced stealth technologies dedicated to reducing their cross-sections to radar, Virginia-class subs are utilizing a piece of kit that can do the same for sonar. The Virginia’s ultra-low acoustic signature comes courtesy of a special anechoic coating. The coating, which consists of a series of sound-absorbent, rubberised panels that sit on top of the hull work by dampening electromagnetic waves, reducing the number that bounce back and sapping their overall energy. Adding to the Virginia’s stealth ability is its revolutionary pump-jet propulsion, which works by drawing water into a turbine-powered pump via an intake then pushing it out at the rear, dramatically muffling noise.