would be better able to penetrate a hull by concentrating their explosive energy over a relatively small area of the target hull. Shaped charges can significantly reduce the amount of explosive needed to achieve the desired level of lethality. As pointed out above, a reduction in warhead weight might be used to enable improvements in other important weapon performance characteristics.

Under ONR sponsorship, progress has been achieved in the safety, arming, and fusing of undersea weapons. With the use of advanced commercial electronics and microelectromechanical systems, the volume of the exploder has been reduced by more than 80 percent. While a reduction in the size of the fuse is important in all explosive-carrying undersea weapons, it is essential to the development of the new 6.25-in. antitorpedo torpedoes.

Modeling of warhead-target interactions is another important area of study that ONR sponsors. These models are important adjuncts to experimental programs, as they will enhance understanding of the physics of the process, reduce the costs of development, and provide estimates of warhead lethality in situations that are difficult to test.

The committee noted that ONR research on explosives should be applicable also to sea mines. No example of this aspect of the research was presented.

Finding: The programs on warheads at the Naval Surface Warfare Center, Indian Head are good examples of research and development (R&D) in a mature area that has consistently delivered fresh results in S&T and new generations of explosive compounds tailored to the Navy's needs. Current research on the penetration of hardened hulls is important. Research on the problems of sensitivity of high-energy materials should be supported.

Much of the volume and weight of torpedoes is usually taken up by the energy and propulsion systems, so it is obviously important to emphasize the S&T base of these systems. In addition, the energy and propulsion systems are usually the noisiest components in most torpedoes.

Current torpedoes use the monopropellant OTTO-fuel II for MK-46 and MK-48 torpedoes and the Stored Chemical Energy Propulsion System (SCEPS) for the MK-50 torpedo. The OTTO-fuel II system operates as an open cycle and discharges the exhaust to the ocean, while the SCEPS system has a closed-cycle engine, a constant overall weight, higher energy density, and less radiated noise.

The absence of atmospheric oxygen provides a challenge for many energy systems in undersea vehicles. Other oxidants must be used, such as sulfur hexafluoride (SF₆) in the SCEPS unit, and there is only limited experience with such systems. Reliability and safety are important concerns for these energy sources because of their novelty and because these systems usually involve very energetic reactions. Cost and the difficulty of maintenance with SCEPS were cited as reasons for replacing the MK-50 engine with that from the MK 46 in the MK-54 torpedo.

The ONR program for the propulsion of undersea weapons has two main thrusts: low-rate energy sources and high-rate energy sources. The low-rate energy sources would be used in unmanned underwater vehicles (UUVs) targets, small delivery vehicles, and other low-speed vehicles, while the high-rate energy sources would be used in high-speed weapons. Energy sources that can be switched from a low rate to a high rate would be applicable in weapons that have a low-speed search mode and high-speed attack.

The conventional low-rate energy sources are electrochemical devices such as rechargeable batteries and fuel cells. ONR activities are concentrated on high-energy-density electrochemical systems, including rechargeable lithium batteries and the new semifuel cells. The semifuel cell is intermediate

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)