Undersea warfare has changed considerably since Admiral Farragut gave his famous battle order over a century ago. Human ingenuity and advancements in technology have taken underwater weapons from floating mines and spar torpedoes to the fast-moving, self-guided, homing torpedoes we have in the fleet today. From submarine warfare to warship design and tactics development, the modern torpedo is one of the fundamental drivers of 20th century naval warfare. Its ability to sink ships and submarines with one shot is always in the mind of naval commanders. For the U.S. Navy, the modern torpedo enables submarines to defeat surface and undersea threats and gives surface ships and aircraft the means to reach beneath the surface and attack submarines.
Building a Better Torpedo
The MK48 Advanced Capability (ADCAP) Heavyweight Torpedo, along with the MK46 Mod 5 and the MK50 Lightweight Torpedoes, are currently the workhorses of the fleet. The heavyweight torpedo is the submarine's key multi-mission underwater weapon, capable of performing both anti-submarine and anti-surface roles. The MK48 Mod 5, with its improved guidance system, and the MK48 Mod 6 with low-noise propulsion, provide the fleet with torpedoes whose performance is unmatched in deep-water scenarios. The lightweight torpedo gives surface ships, airplanes, and helicopters the means to destroy threat submarines. The MK54 Lightweight Torpedo will bring considerably improved shallow water capabilities to the fleet in 2003.
Building on the success of the ADCAP torpedo, new weapon technologies are being developed to tackle the challenging shallow-water littoral environment. These technologies will be common to both the heavyweight and lightweight torpedoes to keep costs down and maximize performance across the board.
Since the end of the Cold War, submarine missions have largely moved from deep water to shallow-water littoral areas. Acoustic reverberation, poor sound propagation, local ship traffic, false targets, and bottom clutter all make torpedo operations more difficult in this noisy operating environment, and the need for more capable guidance and control becomes critical. The Common Broadband Advanced Sonar System (CBASS) upgrades to ADCAP will extend the current sonar array on the weapon into a broadband mode and improve the onboard signal processing to provide enhanced operation against countermeasures and diesel submarines operating in the littorals.
The Next Move: Toward a Smarter Torpedo
At a time when the capabilities of both threat weapons and platforms are developing rapidly, it is crucial to lay the technological groundwork that will facilitate major hardware and software improvements for our next-generation weapons systems. There are several new approaches under study to build "smarter" front-end guidance and control systems for the torpedo. In addition to improved signal and tactical data processing, progress is being made in connectivity between submarines and weapons, intelligent controllers, and ultra-broadband arrays. Acoustic and fiber-optic communications will provide the connectivity to allow fusion of torpedo sensor data with platform information to yield an improved tactical picture for combat control systems. An intelligent torpedo controller will enable the weapon to adapt to dynamic situations, using neural nets and fuzzy logic, and an ultra-broadband array will dramatically improve its sonar capabilities.
The Office of Naval Research (ONR) is supporting new, advanced technologies to solve emerging fleet problems by developing and delivering solutions to the operators in the shortest possible time. One new prototype torpedo, developed as part of their "Swamp Works" effort, will house an ultra-broadband, multi-beam array, which in conjunction with new waveforms, signal processing algorithms from the CBASS program - and improved torpedo tactics - will allow for greatly improved countermeasure rejection in shallow water, while maintaining current performance in deep water. Overall, by using transparent array technology in a new front end, with many more narrow beams to resolve closely spaced objects and countermeasures, this combination will provide a quantum improvement over today's torpedo effectiveness. This will be done initially by installing a new transducer array in front of the existing sonar system, to which it will be functionally transparent. The technology will be applicable to both lightweight and heavyweight torpedoes, and the half-length torpedo currently under evaluation will not only demonstrate this new array but will lead to a formidable new littoral weapon.
Quiet as a Mouse
Developing a truly stealthy torpedo will provide more approach-and-attack options for our submarines. A stealth weapon that cannot be heard until very late in the encounter will delay the threat's detection of the torpedo and impair its ability to respond effectively with either countermeasures or return fire. This will greatly increase the probability of killing the enemy and avoiding a potentially lethal counterattack.
The MK48 Mod 6, while a quiet weapon, still alerts a target when it begins active pinging at the "enable" point. To solve this problem, we are developing advanced passive homing techniques, covert active waveforms with LPI (Low Probability of Intercept) and LPR (Low Probability of Recognition) properties, and associated signal processing. To fully exploit these enhancements, however, a further reduction in radiated noise from the propulsion system is required. Under consideration for the stealth torpedo is a quiet electric or hybrid propulsion system employing the Integrated Motor Propulsor (IMP). The IMP incorporates a radial-field electric motor directly into the torpedo propulsor, thereby completely eliminating an internal motor, through-hull shafts and seals, and creating a single connection point to the hull, where advanced isolation can be utilized for increased stealth. This closed-cycle propulsion will be quiet, wakeless, and depth-independent. And, with a rechargeable energy source, it will help reduce exercise expenses to provide more training opportunities and/or lower total ownership cost. Additional quieting will be achieved using active noise-cancellation techniques.
The Need for Speed
As these new torpedo technologies take shape, they promise some dramatic departures from the configuration of our current weapons. Pushing the speed envelope, for example, will greatly affect torpedo performance and resulting effectiveness - the ability to kill a target before it can react provides a distinct advantage.
Some technical innovations have so significant an impact on our way of doing business that they are often described as "disruptive technologies," with the potential to change the future. One of these disruptive technology concepts in development within undersea warfare is an autonomous high-speed, highly-maneuverable homing torpedo capable of speeds up to five times that of the MK48. Using "supercavitation" techniques, the torpedo becomes an underwater missile, capable of reaching its target before the threat can respond. In this approach, the water near the tip of the projectile - or torpedo - literally vaporizes from the high speed, producing a pocket in which to "fly" the weapon underwater. Traveling in such a vapor pocket provides dramatic reductions in drag, which allows developing extremely high velocity for a given input power. Such a weapon would be well suited for close-range submarine encounters. With multi-purpose configurations, it could be used not only for anti-submarine warfare, but also as an anti-torpedo torpedo, or for defense against high-speed surface craft.
A Key to Survival
Maximizing the survivability of the warfighter is crucial, and self-defense systems are necessary to ensure that all platforms have the capability to protect themselves from attack. Anti-torpedo torpedoes will provide our future platforms with an additional defense capability. Their primary mission is to destroy incoming torpedo threats that may have gotten through a countermeasure field. Based on technology under development at ONR, a 6.25 inch-diameter self-protection weapon is under study for the defense of surface ships and submarines using supercavitation technology. The Advanced High Speed Underwater Munition (AHSUM) program has already demonstrated the effectiveness of such high-speed underwater bullets. Fired from an underwater gun, these projectiles have successfully broken the speed of sound in water (1,500 meters per second), bringing their future application much closer to reality. The Navy is already developing a mine-clearance system that uses supercavitating bullets fired from a helicopter. The Rapid Airborne Mine Clearance System (RAMICS) targets mines at shallow depths and delivers bursts of armor-piercing rounds from the air, through the intervening water, and into the mines. Merging RAMICS with AHSUM could provide the Navy with a multi-purpose round capable of engaging a range of mine-like targets from above or beneath the ocean surface.
The Naval Undersea Warfare Center has developed a comprehensive vision that supports both current Navy needs and those well into the future. The technologies needed to support this vision are identified above. In today's limited funding environment, it is important to focus on the technologies that provide needed future capabilities.
A Bigger Bang
Torpedo payloads will also see improvement in the future. Warheads will be capable of multi-mode detonation, offering both bulk-charge and directional alternatives. They will provide higher lethality and use increasingly energetic materials to create more powerful effects, while still meeting the requirement for insensitive munitions. This would provide the torpedo more "bang for the buck," and provide the potential for weapons to be smaller and lighter, with increased range capability or room for additional sensors and signal processing.
Using "supercavitation" techniques, the torpedo becomes an underwater missile… the water near the tip of the projectile – or torpedo – literally vaporizes from the high speed, producing a pocket in which to "fly" the weapon underwater.
The Future
The operating environment for torpedoes continues to change. Undersea networks for communications, sensors, and tactical engagement continue to develop through advances in acoustic communications and fiber-optic links. Fusion of data from platform, weapon, and off-board sensors will require a next generation of torpedoes that can communicate with the network and benefit from intelligent control. They may be deployed not only from submarines, but also from unmanned undersea vehicles that become remote firing platforms and keep the submarine out of harm's way.
Since the Navy's entry into torpedo research and development in the 1860s, the success of our modern torpedoes has been one of our proudest accomplishments. This has been a joint effort, working with Navy sponsors, academic and industrial partners, allies, and the fleet. The community leverages the efforts of all the participants and brings new technology to the fleet sooner and cheaper. As we build the bridge to the future, we will continue these efforts to make the best of our technology a reality and to provide the U.S. Navy with the underwater weapons capability it needs to be first in the world.
This illustration shows the weapon envelope for today's heavyweight and lightweight torpedoes, as well as potential future weapons designed for greater stealth and speed, and in support of defensive weapons concepts.
To take advantage of new Common Broadband Advanced Sonar System (CBASS) technology, an advanced acoustic array will form multiple narrow beams, capable of discriminating spatially between targets and countermeasures. The resulting ultra-broadband, low-noise sonar will provide significantly improved homing performance in littoral environments, and new array fabrication techniques will make these advances affordable.
The heart of the Integrated Motor Propulsor is a radial-field, rim-driven electric motor integrated directly into the tail-cone propulsor assembly. This eliminates the need for a separate internal electric motor, facilitates a simpler interface with the rest of the torpedo, and creates opportunities for reduced length, greater reliability, and lower noise.
Bernard Myers is the Deputy Technical Director at the Naval Undersea Warfare Center (NUWC); Frederick Cancilliere is the Program Manager for Torpedo, Countermeasure, and UUV Science and Technology at NUWCDIVNPT; Kenneth LaPointe is the Undersea Warfare Analyst for NUWCDIVNPT. Other contributors to this article include Jontay Jeong, from the Torpedo, Countermeasure, and UUV Science and Technology Staff; and Candida Desjardins, a member of the NUWCDIVNPT Communications/Customer Relationship Management Staff.
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