Unmanned Underwater Systems = Force Multiplier

Speaking at the Surface Navy Association’s annual symposium in Crystal City, Virginia, on Jan. 9, the new Chief of Naval Operations Adm. Lisa Franchetti released her priorities for “America’s Warfighting Navy,” and talked about putting “more players on the field.”

“We must think, act, and operate differently, leveraging wargaming and experimentation to integrate conventional capability with hybrid, unmanned, and disruptive technologies,” she said. “Tomorrow’s battlefield will be incredibly challenging and complex. To win decisively in that environment, our Sailors must be the best warfighters in the world with the best systems, weapons, and platforms to ensure we can defeat our adversaries. We will put more players on the field—platforms that are ready with the right capabilities, weapons and sustainment, and people who are ready with the right skills, tools, training, and mindset.”

Getting more players onto the field calls for a “distributed fleet architecture” of both manned vessels and unmanned systems to spread the Navy’s capabilities over an increased number of platforms. They are a force multiplier.

According to a report issued Dec. 20, 2023, by the Congressional Research Service, the Navy is moving to a more distributed fleet architecture, “meaning a mix of ships that spreads the Navy’s capabilities over an increased number of platforms and avoids concentrating a large portion of the fleet’s overall capability into a relatively small number of high-value ships (i.e., a mix of ships that avoids ‘putting too many eggs into one basket’).”

To meet that goal, the U.S. has a lot going on in the undersea domain, including unmanned underwater vehicles (UUV), manned submarines, and torpedoes and other weapons.

Maritime drones come in a variety of shapes and sizes to meet a broad spectrum of requirements, such as surveillance and environmental sensing; laying mines or finding mines; to neutralizing enemy swimmers and blowing up targets. The U.S. Navy’s efforts to develop, test and field new autonomous unmanned platforms and capabilities at sea spans a spectrum from small, hand-carried unmanned UUVs, to surface ship and submarine launched torpedoes, to the extra-large UUVs, all the way to the manned submarine fleet.

Large UUVs

The largest UUVs are the Boeing XLUUV and Snakehead LDUUV.

The Navy accepted delivery its first Extra Large Unmanned Undersea Vehicle (XLUUV) Test Asset System in December. The Boeing Orca XLUUV, designated XLE0, from the manufacturer Boeing.

In addition to the test vehicle, five more Orcas are being built. A December 2023 news release from By Program Executive Office Unmanned and Small Combatants, stated that XLE0 began in-water testing in Spring 2023 in Huntington Beach, California. “Lessons learned from XLE0’s testing will be applied to Orca XLUUV 1 through 5, which will be built and delivered to the Navy in the future,” the release said.

A Boeing press release said the Orca is “a new class of autonomous submarine that can perform long duration critical missions to achieve undersea maritime dominance in changing environments and contested waters.”

The Orca XLUUV is a cutting-edge, autonomous, unmanned diesel-electric submarine with a modular payload section to execute a variety of missions critical to enhancing the Navy’s undersea prowess. Configured to accommodate various payloads, the Orca XLUUV allows for the seamless integration of sensors, communication systems, and other mission-specific components, adapting to the evolving requirements of naval operations.

for sustained operational presence and increased mission effectiveness in challenging undersea environments.

Orca is based on the Boeing Echo Voyager XLUUV. Like Echo Voyageur, Orca is 51-feet long, but features modular construction to allow for the insertion of an additional 34-foot payload module.

According to the Congressional Research Service “Navy Large Unmanned Surface and Undersea Vehicles: Background and Issues for Congress” report issued on Dec. 20, 2023, “the Navy wants to use XLUUVs to, among other things, covertly deploy the Hammerhead mine, a planned mine that would be tethered to the seabed and armed with an antisubmarine torpedo, broadly similar to the Navy’s Cold War-era CAPTOR (encapsulated torpedo) mine.”

Also in the large category, the Snakehead is a tube-shaped UUV, about four feet in diameter and eight feet long. The Navy refers to it as a “modular, reconfigurable, multi-mission underwater vehicle deployed from submarine large ocean interfaces, with a government-owned architecture, mission autonomy and vehicle software.” The preliminary design was done by Naval Undersea Warfare Center at Newport, and the plan was to hand off construction to a competitively-awarded prime contractor. The first Snakehead was “christened” at NUWC Newport in September 2022, but the program is on hold for the time being.

Medium UUVs

Leidos and L3Harris are working on a medium-sized unmanned undersea vessel (UUV) for intelligence, surveillance and reconnaissance (ISR) for the submarine force and the explosive ordnance disposal community.

The Razorback UUVs were designed to operate from a dry deck shelter or from a craft of opportunity. Razorback is based on the HII REMUS 600 platform. The newest version will be deployed from a submarine torpedo tube and be fully integrated into the submarine’s combat system. This new capability basically means any submarine can become a host platform for UUVs.

The Knifefish medium-class UUV is designed as part of the littoral combat ship mine countermeasures mission package. It can search a large area and can detect, classifying and identifying mines, especially the hard-to-find bottom and buried mines in high clutter environments. Knifefish uses the low-frequency broadband capability developed by the Physical Acoustics Branch of the Naval Research Laboratory. The 2,000-lb., 22-foot long Knifefish is based on the Bluefin 21 UUV. It’s sized for a 21-inch submarine torpedo tube, Knifefish is intended to be launched by a surface craft. According to the manufacturer, Knifefish will reduce risk to personnel by operating within minefields as an off-board sensor while the host ship stays outside the minefield boundaries.

Although it has passed its milestones, the MCM mission package being delivered to the Independence variant LCS does not yet have the Knifefish system.

Small UUVs

The Navy’s expeditionary forces can deploy with small UUVs for underwater survey or mine countermeasures, and can operate from land or various craft of opportunity. Man-portable UUV s are available on the market, including the General Dynamics Mission Systems Bluefin Robotics Bluefin-9 and HII Remus 100 and 300.

Offensive Mines

The U.S. inventory of sea mines is either dropped by aircraft, such as the Quick Strike family of mines, or covertly deployed by submarines like SLMM and Hammerhead. Quick Strike are basically air dropped bombs with special fusing mechanisms that can wait to be detonated under the right circumstance. Submarines can carry the MK 67 submarine launched mobile mine (SLMM) is based on the MK 37 torpedo. It can clandestinely swim to a pre-determined location where it waits until target criteria are met, at which time it detonates.

The Hammerhead undersea mine is also submarine launched and can be delivered to a location where it sits and wait until a target is detected. It is based on the Cold War-era CAPTOR mine, which stood for “enCAPsulated TORpedo,” which was armed with a MK 46 lightweight torpedo, and could operate at depths up to 1,000 feet.

Hammerhead consists of a mooring module that plants itself on the bottom; the power and sensing modules; and the business end, which is a Mark 54 Lightweight homing torpedo. This is a 600-pound weapon with a range of at least six miles widely used by the U.S. Navy and others for anti-submarine operations. (Anti-ship torpedoes are several times larger).

General Dynamics Mission Systems was issued a $93 million contract in 2021 to design, test and deliver the “Hammerhead Prototype encapsulated anti-submarine warfare mine system.”

The new Hammerhead differs from CAPTOR in two important ways. One is that remote control capability, which means it can legally be positioned in peacetime.

The location of air-dropped Quick Strike mines can be observed, while Hammerhead can be surreptitiously and strategically placed at choke points, sea lanes, or near enemy submarine ports.

Another new submarine deployed mine is system is the Mining Expendable Delivery Unmanned Submarine Asset (MEDUSA).

The Navy’s Unmanned Maritime Systems Program Office (PMS 406) is developing the system to “address the need for an advanced maritime mining system with long-range offensive mining capabilities.”

The Navy has said that the Orca XLUUV could also deploy MEDUSA to conduct offensive mine warfare.

The Navy has an active tender out to industry to deliver the MEDUSA system.

Submarines

The current attack submarine fleet includes 26 of the 62 Los Angeles-class submarines built for the Navy and commissioned between 1976 and 1996. The lead ship in the class, USS Los Angeles (SSN 688) was commissioned Nov. 13, 1976. The newest, USS Cheyene (SSN 773), is now 27 years old.

USS La Jolla (SSN 701) was decommissioned in 2019, but continues to serve as a moored training ship (MTS 701) and the Nuclear Power School in Charleson, S.C. Likewise USS San Franscisco was decommissioned in 2022 and is now MTS 711 at Charleston. Some of the 688s were pulled from service at their mid-life point rather than incur the expense of the costly mid-life refueling. San Francisco was in commission for more than 41 years, while USS Baltimore (SSN 704) served for just 15 and a half years of active service.

Los Angeles-class submarines carried MK-48 heavyweight torpedoes, submarine launched mines, and both Tomahawk and Harpoon missiles. Later ships in the class had vertical launch missile tubes located forward of the pressure hull to extend their weapons-carrying capacity.

Both Newport News Shipbuilding in Virginia and General Dynamics Electric Boat in Connecticut built the 688s. They are the only two shipyards that build nuclear powered ships in the U.S. Newport News was also building Nimitz-class nuclear powered aircraft carriers. while and EB was building the Ohio-class of ballistic missile submarines during this time.

The SSN-21 Seawolf class was intended to follow the 688s as the next generation of attack boats for the 21st century, and designed for the Soviet Navy threat.

Originally 29 were to be built, but only three were completed, with the third, USS Jimmy Carter (SSN 23) was built with facilities for carrying special operations vehicles and unmanned systems, as well as the ability to operate near the bottom to conduct special tasks.

As the Cold War ended, the need for the capability have way to the less capable and expensive USS Virginia class (SSN 774) class. The current program of record is for 66 boats, with 23 now active in the fleet. The lead ship was commissioned in 2004, and the newest, USS Hyman G. Rickover (SSN 795) joining the fleet in October of 2023. Newer versions will be fitted with the Virginia Payload Module (VPM) within a 70-foot hull section to carry Tomahawk cruise missiles and the Conventional Prompt Strike hypersonic missile.

Like the 688s, the Virginia-class boats are built in both Huntington Ingalls Industries Newport News Shipbuilding and General Dynamics Electric Boat shipyard.

Three additional Virginia-class boats will be built for Australia as part of the trilateral Australian-British-American security pact known as AUKUS. Eventually Australia will build the future SSN-AUKUS class submarines in Australia.

To test and refine the designs for the Seawolf and Virginia class submarines, the Navy built Large Scale Vehicles (LSVs), operated by the Naval Surface Warfare Center Carderock Division’s Acoustic Research Detachment (ARD) on Lake Pend Oreille in Bayview, Idaho. Kokanee (LSV 1) is an unmanned, powered one-quarter scale model of the Seawolf (SSN-21). Cutthroat (LSV 2) is one-quarter-scale model of the Virginia-class boats, and is the world's largest underwater autonomous submarine vehicle. They are used as demonstrator vehicles for testing the hydrodynamic and acoustic properties of the hull design and other advanced technologies. Following the end of the Cold War and the establishment of treaty limitations of submarine launched ballistic missile warheads, the Navy took four of its 18 Ohio-class SSBNs and converted them to conventional cruise missile carriers. The first four Ohio-class boats, 727 to 729, received the conversion between 2002 and 2008. Instead of 16 Trident missiles, they carry 154 conventional Tomahawk land attack missiles, and have the ability to covertly deploy special operations personnel and equipment. The remaining 14 Ohios had four of their 24 missile tubes deactivated to meet the treaty obligations.

The lead ship of the class, USS Ohio (SSBN 726), was commissioned in 1981. She underwent a conversion and reclassified as SSGN 726, rejoining the fleet in 2006. The newest, USS Louisiana (SSBN 743), was commissioned in 1997.

The Ohio Replacement Submarine (SSBN-X), now known as the Columbia-class, will begin to enter service in 2031. The lead ship, USS District of Columbia (SSBN 826), honors the nation’s capital city. The Columbias are designed for a 41-year service life, with an expected completion of 124 strategic deterrent patrols. The new SSBNs share roughly similar dimensions (length and displacement) with the Ohios; much of its strategic weapon capabilities with the Royal Navy’s Dreadnought class of SSBNs; and have similar sensors as the Virginia-class attack boats.

Torpedoes

Torpedoes come in two basic sizes— heavyweight and lightweight.

The Navy arms its submarines with heavy-weight 21-inch (diameter) MK48 torpedoes. Surface ships, maritime patrol aircraft and ASW helicopters use the lightweight 12.75-inch MK46, MK 50 or MK 54 torpedoes.

Many UUVs are designed to be deployed from submarines. To be carried about subs and launched while submerged, many UUVs resemble torpedoes.

Mk-48 and Mk-48 ADCAP (advanced capability) torpedoes are made by Lockheed Martin, and are wire-guided, which means they can get constant updates regarding the target and course to intercept. They can also operate without the wires, using their own active or passive sensors. They are programmed to detonate right below the target, breaking its keel.

Made by Raytheon, the MK 54 is the current lightweight torpedo, although Mk 46 and MK 50s can be found in use. These weapons are launched over the side of surface ships with the ubiquitous MK 32 surface vessel torpedo tube launcher, or dropped into the water by aircraft.

Both the lightweight and heavyweight torpedoes use OTTO II fuel and PBXN explosives in the warhead.