GAO Report on Navy alternate propulsion systems

Report to: Roscoe G. Bartlett, Chairman Subcommittee on Projection Forces, Committee on Armed Services
As the Navy looks to design an affordable force that is capable of meeting future security challenges, some of the assumptions and factors that have guided past Navy decisions on propulsion systems may require reassessment. For example, technological advances have enabled greater efficiency in both nuclear and conventional propulsion systems. Moreover, the cost of fossil fuel has risen sharply in recent years.

According to Office of Naval Research officials, improvements to electrical components will generally improve fuel efficiency and overall mission effectiveness of future Navy surface ships. For example, superconducting motors, using special wiring to lower the resistance of electricity flow and employing cryogenics to reduce temperatures within the motor, will be more powerful and smaller, thereby reducing weight and saving onboard space for other purposes. High-speed generators, also projected to be smaller, will make it possible to couple high-speed gas turbine engines directly to the generators without the use of reduction gears, thereby reducing weight, saving space, and making the engines more fuel efficient. Eliminating these reduction gears will also help future ships to be quieter and consequently more difficult to be detected by enemy forces. The Office of Naval Research is also conducting research into fuel cell technology. Germany recently produced two submarines with fuel cell propulsion systems, but a Navy official said that nonnuclear submarines do not meet the mission requirements of the United States Navy. Additionally, these fuel cells use onboard hydrogen in its natural state, which is difficult and dangerous to store in large quantities. Conversely, the fuel cell technology the Office of Naval Research is pursuing involves extracting hydrogen from diesel fuel, which can be safely stored and transferred at sea, according to the official. The hydrogen is used to produce electrical power without the use of diesel or gas turbine engines. The use of fuel cells would also permit a ship’s power system to be dispersed throughout the ship, increasing the ship’s ability to survive if attacked, according to Navy officials. Office of Naval Research officials stated that fuel cell technology is promising for naval application and has already completed some prototype testing. However, officials stated that the technology is at least 3 to 5 years away from acquisition consideration.

GAO