between a battery and a fuel cell. It has aluminum (or magnesium) anodes that are consumed during operation and an oxidant that interacts with the catalytic cathode.

Research is also being conducted using thermal units to provide low-rate energy sources. The thermal conversion activities include the development of a small, closed-cycle Stirling engine coupled to a lithium-sulfur hexaflouride thermal-energy source. A novel wick combustor is being developed for this unit using capillarity to distribute the liquid metal.

High-rate energy sources are being evaluated for potential use in torpedoes and in countermeasure applications. There are two main ONR activities in this field, HYDROX, a hydrogen and oxygen producer and combustor, and an aluminum-water vortex combustor for a water ramjet.

The HYDROX energy system produces gaseous oxygen from liquid lithium perchlorate and hydrogen from the reaction of water and a lithium-aluminum alloy. The gaseous hydrogen and oxygen produced are burned in a combustion chamber to produce steam for a closed Rankine-cycle system. The same gas source could provide the hydrogen and oxygen for a fuel cell. The gases could also be used in a combined system utilizing a low-power unit for low-speed search and a high-power unit for high-speed operations. The innovative wick system to distribute liquid metal is being developed for use in the SCEPS (lithium-sulfur hexafluoride) upgrade.

A novel vortex combustor is being developed for the water ramjet that would propel the high-speed supercavitating vehicle. Aluminum particles are burned in a vortex arrangement in a reaction with water. This unit, although potentially useful as a source of high-density energy for the supercavitating ramjet, could be used in other applications. The production of large volumes of gaseous hydrogen from the aluminum-water reaction could, perhaps, be utilized to increase the energy density.

The high-rate-wick Stirling engine can be employed in torpedoes and manned undersea vehicles and/or UUVs to enhance range, speed, and endurance. The HYDROX system could be used in high-rate, low-rate, or hybrid modes to enable smaller vehicles or superior performance. The aluminum-seawater vortex device could provide very high speed in special applications. These innovative approaches are good examples of revolutionary technology from ONR programs.

Other propulsion S&T efforts include those on electrochemical energy sources, including fuel cells at the Naval Undersea Warfare Center (NUWC), Naval Surface Warfare Center, Carderock Division (NSWC/CD), and several small academic and industrial contractors. The electrochemical area is the largest component of the undersea weapons 6.1 budget ($2 million in FY99). Another effort is that on underwater propellants at the Naval Surface Warfare Center, Indian Head (NSWC/IH).

Finding: The program on propulsion at the Applied Research Laboratory, Pennsylvania State University (ARL/PSU) is exemplary and offers technologies for both weapons and vehicles that could be used in future systems. Closed-cycle engines are among the increasingly attractive options as the importance of stealth and endurance increases.

The operational effectiveness of modern torpedoes has eroded in the face of countermeasures, reflected clutter (or reverberation) in shallow water, and the diminishing strength of acoustic targets. The core issue is the ability of the torpedo's guidance and control system to separate an actual target signature from clutter, whether generated by countermeasures or as a reflection from the environment. During the Cold War, quieting and countermeasures were the major challenges. Now, quiet and small diesel-electric submarines and high ambient noise levels in the littoral shallow waters result in severe problems for target acquisition and homing, including the following:

Front Matter (R1-R12)

Executive Summary (1-5)

1 Introduction (6-10)

2 Assessment of the Office of Naval Research's Undersea Weapons Science and Technology Program (11-37)

3 The Future of Navy Undersea Weapons: Important Issues (38-43)

4 Findings, Conclusions, and Recommendations (44-46)

Appendix A Technology Insertion Road Map (47-50)

Appendix B Lessons of the Advanced Rapid COTS Insertion Process (51-51)

Appendix C Biographies of Committee Members (52-55)

Appendix D Acronyms and Abbreviations (56-58)