By Katherine Owens -- Warrior Maven Editorial Fellow

The Navy’s submarine fleet and undersea warfare experts are part of the select group seeking to understand the depths of the ocean and the sea floor. The seabed and deep-ocean are some of the least explored places on the planet and it is the next frontier for those members of the Office of Naval Research (ONR) seeking to achieve superiority in the underwater theater.

Naval undersea innovation is geared toward domain control, which encompasses two significant areas for advancement. The first, as stated by the ONR’s Full Spectrum Undersea Warfare (FSUSW) program, is increased operational effectiveness; and the second is detection capability.

Power Supply Technology for UUV's

The key to advancing any undersea vessel’s capabilities is advancing its power supply technology. The Defense Advanced Research Projects Agency (DARPA) is one of the agencies taking the lead on developing new power supply hardware for unmanned underwater vehicles (UUVs). 

UUV Manta Ray

Manta Ray

Technology currently in development by DARPA and its partners will no longer rely on high-density batteries nor will it use nuclear power.

DARPA’s collaborative publication with ONR in the subject explains, “Greater breadth of mission profiles for current and future Naval UUVs require longer endurance stealthy propulsion systems that extend the current capability of 10-40 hours to several days or weeks. Current and future anticipated technologies based solely on high energy density batteries will not provide adequate endurance for the mission.”

According to DARPA, advanced UUV power supply technology will be capable of operating up to four hours on maximum power and operating under ideal conditions for 1,680 hours. At the same time, the latest technology is expected to be able to perform while emitting minimal sound waves, so as to avoid detection by enemy sensors.

Hybrid Fuel Cell Solution

ONR has proposed fuel cell or combustion technology as possible replacements for traditional batter power. A case study sponsored by Lynntech also shows that a hybrid fuel cell solution could be a viable option. 

In a hybrid fuel cell system, a hydrogen fuel cell is supported by a traditional battery. The hydrogen fuel cell would use polymer electrolyte membrane (PEM) technology, where a combination of cathodes and anodes separate the protons and electrons of the hydrogen molecules and the PEM forces the electrons to travel through a circuit to generate power. 

According to Lynntech’s published research, the smaller, traditional battery will offer supplemental power when necessitated by the size of payload. Meanwhile the hydrogen fuel cell would “provide power at a stable rate for the base load and recharge the small battery during low power intervals.”

Payload and Payload Delivery Systems

In addition to enhanced power systems, another way FSUSW is pursuing heightened efficacy is through the Innovative Naval Prototype (INP) program’s three FY 21 projects focused on payload and payload delivery systems. 

“Payload” may refer to weapons, UUVs, or even surveillance or sensory devices. In accordance with ONR’s strategy of combining both existing and newly developed hardware and software, advanced payload delivery systems are integrated with already existing or simultaneously developed UUVs.

Within the past decade, a major step toward integrating new payload delivery systems with existing software on undersea vessels was the introduction of the Flexible Payload Module (FPM).

“[The FPM] approach uses a new network-based command and control system to facilitate communications between the ship and a wide range of payloads,” according to an ONR-sponsored paper published by the University of Washington Applied Physics Laboratory, “FPM technology represents a new paradigm in payload integration.”

Communications

As the FPM demonstrates, a critical component of effective payload delivery is communication. The primary mechanism used to transmit information between submerged vessels, including UUVs and submarines, and air support is acoustic communication. 

Acoustic signal pathways include the water, seabed, and surface of the ocean. On the surface, sonobuoys are often used to house transducers, or devices that convert energy from one form to another, and serve as nodes between air and undersea systems. 

At the receiving node, the data stream is converted from electrical signals into acoustic signals. The data is amplified, modulated, and then decoded. At the transmitting node, the opposite conversion sequence occurs.

As noted in a previous Warrior Maven article, undersea communication has been an ongoing challenge. In a paper for the Journal of Physics, Nvzhi Tang et al describe how undersea turbulence, internal waves, varying water masses, uneven seabed, and natural ocean noises can all disrupt acoustic transmission. 

However, Sara Pensieri and Roberto Bozzano of the Italian National Research Council’s Institute of Studies on Intelligent Systems argue in Underwater Acoustics that the tumultuous ocean environment can also support and enhance underwater acoustic communication. For example, the stratification of the ocean into different layers is also a major factor in acoustic transmission. 

Pensieri and Bozzano describe how the diurnal cycle, seasons, and weather conditions all influence ocean temperature, which in turn leads to stratification. 

During colder seasons, surface water becomes colder and sinks, allowing warmer water to come to the surface. This exchange of water masses results in a “mixed layer” where the temperature is more or less constant. This homogenous temperature zone allows for a fixed sound velocity, which makes acoustic transmissions more consistent.

Recommended Articles

Current acoustic and other undersea communication research examines ways to achieve this consistency under any conditions, particularly with experiments in long-range and low-speed communication technology and increased collaboration with other observational, communication, and payload delivery systems.

The SonoFlash Sonobuoy 

One recent advancement in this area is the sonobuoy developed by Thales, the SonoFlash. The SonoFlash represents the next generation of buoy-enabled undersea communication because of its advanced acoustic technology and capacity for multi-static anti-submarine warfare. 

Acoustic innovations in the SonoFlash give it both active and passive sonar capabilities. Passive acoustic devices “listen” to and record sound pressure levels (SPLs) that can then be used to calculate spatial and geographic data. 

SonoFlash SonoBuoy

Impression of SonoFlash Sonobouy at sea

Active acoustic signaling involves the device emitting a signal at a certain frequency and then quantifying the data produced as the sound waves travel and bounce off obstacles.

Alexis Morel, Vice President of the Underwater Systems at Thales explains, “navies will be able to rethink their approach and operational concept. In addition, we selected for the SonoFlash a low frequency between three and four kHz...This provides the end user with great detection ranges.”

As a component of full spectrum undersea warfare, the SonoFlash would function as an integral node of cross-platform communication systems, such as the Networked Persistent Undersea Surveillance (PLUSNet) System.

PLUSNet is another innovation designed to increase and enhance the detection and communication necessary for undersea dominance. PLUSNet is based on the idea of a distributed sensor field. It employs both mobile sensors, such as UUVs and Aerial Unmanned Vehicles (AUVs), and fixed sensors, such as Sonobouys, to create a network of acoustic and RF gateway signals that are continuously reporting on the environment and able to adapt to tactical and environmental changes.

Detection Capability

Going hand-in-hand with communication, detection capability is another crucial component of undersea domain control. The vastness and near-impenetrability of the ocean, combined with technological advances, gave submarines the ability to avoid detection starting around the 1940s. 

However, as radar and surveillance technologies become more advanced, maintaining secrecy becomes more difficult. Defense manufacturer Sparton, estimates that at least 41 countries are currently operating submarines.

As collaborators at ONR and the University of Washington wrote, “to address the quiet undersea threat, a sensing system must be covertly deployed in days, operate for weeks to months, and adapt to in situ conditions to provide detection, classification, localization, tracking, and hand-off capability comparable to manned platforms.”

That’s why the Navy’s latest undersea initiatives focus both on achieving greater detection capacities and on evading detection with its own undersea vessels and platforms.

A promising advancement in detection capacity involves improved acoustic technology that operates using lower frequencies, also featured in the SonoFlash sonobuoy. 

Briefly, frequency is a measure of the number of pressure waves traveling past a certain point in a given amount of time. 

According to the National Oceanic and Atmospheric Administration (NOAA), lower frequency signals travel farther because as the sound waves move, they lose less of their energy to the surrounding environment than higher frequency waves, allowing them to travel longer distances. 

Therefore, the low frequency transmissions of the SonoFlash enhance user detection abilities namely because the transmissions have longer range, increasing the chance of encountering foreign entities.

Magnetic Anomaly Detector

Another technology helping to increase undersea visibility is the magnetic anomaly detector (MAD)

These devices are able to detect small changes in the Earth’s magnetic field, such as those caused by the ferromagnetic material of an enemy submarine hull. MADs can be deployed from UAVs and as of 2019, development is underway for a device that could deploy from a P-8A aircraft, according to the Washington Headquarters Services Acquisition Directorate.

"Full Spectrum” Navy Undersea Initiatives

Encompassing technologies from new-age power generators to payload delivery systems to seabed-to-satellite communication “full spectrum” is an apt description for the Navy’s undersea initiatives. 

In strategic terms, these coming advancements toward domain control increase the Navy’s power of deterrence. As Marc S. Stewart of University of Washington’s Applied Physics Laboratory states, “by continuously improving its undersea warfare capabilities through new technologies and CONOPS, the U.S. would create a widening gap that adversaries may not have the money to counter. They may also be deterred from using existing naval forces to engage in conflict.”

In other words, in increasing the Navy’s ability to carry out effective and covert operations from beneath the ocean’s surface, domain control ultimately means decreasing the likelihood of mass underwater conflict.

Katherine Owens is an Editorial Fellow at Warrior Maven. She previously wrote for Defense Systems and holds a B.A. in International Affairs from the George Washington University, where she studied security policy and specialized in arms control and nuclear deterrence. Katherine will be attending Columbia University in Fall 2021 where she will pursue an M.A. in Political Science from the Columbia University Graduate School of Arts and Sciences.