By Scout Warrior Contributor -David Hambling
A new type of miniature torpedo, revealed in patents from Boeing, could transform naval warfare, and anti-submarine operations in particular. Instead of exploding, it burns its way through a ship’s hull like a thermal lance. The tiny weapon, more compact than anything fielded previously, could turn fleets of small unmanned aircraft and underwater vehicles into effective hunter-killers.
Conventional wisdom holds that torpedoes need to be big because they need a large warhead. The US Navy’s standard torpedo is the 3,520-pound Mk 48 and even the ‘lightweight’ Mk 50 torpedo, dropped from aircraft and helicopters, weighs 750 pounds. Boeing’s new torpedo is a minnow by comparison, at less than ten pounds and just eighteen inches long.
Traditionally torpedo warheads have been of two types. The larger ones, like the Mk 48, destroy a vessel by explosive power, with a combination of blast and bubble action: the explosion creates a cavity underneath the ship and the resulting forces can literally break a small ship in half. Smaller torpedoes, like the Mk 50, have a shaped charge, similar to those used on anti-tank weapons, producing a focused jet which punches a large hole through a ship’s hull.
A shaped charge small enough to fit in a ten-pound torpedo would not be effective, so an alternative kill mechanism was developed. Boeing’s torpedo clamps itself to the metal hull with magnetic grippers which keep it perpendicular to the hull – underwater magnetic bugs which attach themselves to submarines have been in use for some time. It then ignites a ‘flammable element’, a magnesium sphere which burns fiercely even underwater. Magnesium burns at such a high temperature that it breaks water into oxygen and hydrogen and burns in the oxygen it releases. A spring-loaded action drives the burning magnesium against the hull so it melts its way through, much like a thermal lance.
The clever part of the design is that the torpedo has a magazine running its entire length containing several of these flammable elements. When the first element burns out after a few seconds, a second one is ignited and applied to the same spot, and keeps going until it melts through – and the mechanism will continue pushing burning magnesium spheres through the hole, even as seawater starts flooding in. A variation of the design has a helical magazine with an even greater number of flammable elements.
The design has obvious limitations.
“It certainly is possible to burn through a hull, but I would guess that the hole would be relatively small,” says Norman Friedman, a prominent analyst and underwater weapons expert at the US Naval Institute. “It would not be enough to sink a large surface ship, which is compartmented.”
Friedman is also skeptical of how effective the weapon would be against some submarines.
“A good-sized hole in a pressure hull might be worthwhile, because water pressure might do the rest of the job, but I don't quite see a burn on the outer part of the hull -- outside the pressure hull in the usual Russian double-hulled sub, for example -- penetrating to the pressure hull.”
The torpedo is described as being able at sink both ships and submarines, but Boeing may not see the torpedo being able to take out a ship on its own, as larger weapons can. Rather, numbers of them would inflict ‘death of a thousand cuts,’ each one taking out a compartment or a section of a submarine until it sinks. This is made explicit in the final section which describes “a plurality of miniature torpedoes” attacking a target.
In spite of its diminutive size, this is not a dumb weapon but has sensors and guidance so that it only needs to be dropped in the “general geographic area” of the target. One version inflates floatation devices, waiting like a mine, or rather an armed sonobouy, until it spots the target: “The deployed flotation devices would support the targeting control apparatus on the surface of the water with the targeting control apparatus suspending the miniature torpedo below the water surface. The control unit would then control the targeting control apparatus to locate the target and then release the torpedo and control the torpedo to travel to the target.”
The designers even intend multiple torpedoes to network and work in a hunting pack to increase their efficiency and the area they can cover:
“The antenna of each targeting control apparatus is extended and transmits signals that are received by the antenna of the other targeting control apparatus and/or by a central command to coordinate an attack by the plurality of miniature torpedoes on the target. By deploying a plurality of miniature torpedoes and their attached targeting control apparatus the targeting control apparatus can track the movements of the target by triangulation.” (My emphasis)
The main stated purpose of the new torpedo is to provide armament for very small unmanned vehicles. Boeing makes a number of small drones for naval use, including the new RQ-21 Blackjack (sixteen-foot wingspan) and Scan Eagle (ten-foot wingspan). These can be flown from any ship, but they are far too small to carry existing torpedoes. At present such drones are only useful for reconnaissance; if armed, they would turn any ship into a miniature anti-submarine warfare platform. The Blackjack, for example, has an endurance of sixteen hours, cruises at 60 mph and could carry two torpedoes. Even a small ship might operate a squadron of them instead of a helicopter.
The miniature torpedo would also greatly increase the weapons load of existing platforms. While not explicitly stated, it its interesting the that size of the new torpedo corresponds roughly to existing submarine-sensing sonobouys, so fields of the torpedoes could be dropped rapidly over a wide area by planes like the P-8 Poseidon.
Boeing politely declined to comment on their torpedo developments, which may indicate that this is an active and sensitive program. The project is described in two similar patents a year apart. The second patent, which had a publication date of April 2015, adds more detail on co-ordinated multi-torpedo attacks, possibly to solve the problem highlighted above.
The company already has a contract for the Navy’s ‘High Altitude Anti-Submarine Warfare Weapon’ an add-on kit which puts wings and a jet engine on the Mk 50 torpedo so it can be delivered from long range and high altitude. The new weapon could also be delivered by similar means – in fact an extended barrier of floating torpedoes could be put in the path of a fleeing submarine. It could also arm fleets of small unmanned underwater vehicles, like the U.S. glider recently ‘kidnapped’ in the South China Sea.
It is impossible to tell how advanced the torpedo plans are, or how well the device will work in practice. Friedman doubts how easily it could stay attached to a fast-moving vessel. Countermeasures might be possible; during WWII, German tanks were covered in an anti-magnetic paste called Zimmerit to prevent magnetic grenades sticking to them – though might interfere with existing anti-sonar coatings.
Swarms of small drones are a growing force in air power, offering enhanced capability at low cost. In parallel with this, air-launched weapons have been getting progressively smaller and smarter. These days a targets can be engaged with a 34-pound AGM-176 Griffin missile or a 5-pound Switchblade rather than a 100-pound Hellfire. Boeing’s new torpedo extends this reach to the seas; in future, submarines may find they are being pursued not by a handful of hunters but by hundreds – or thousands.
David Hambling is a London-based journalist and author with a particular interest in unmanned systems. His book is “Swarm Troopers: How small drones will conquer the world” is out now.