United States Government Accountability Office

Washington, DC 20548 

July 6, 2006 

The Honorable Roscoe G. Bartlett 

Chairman 

Subcommittee on Projection Forces 

Committee on Armed Services 

House of Representatives 

Subject: Propulsion Systems for Navy Ships and Submarines

Dear Mr. Chairman: 

In recent years, the Navy has used nuclear propulsion systems for its submarines and 

most aircraft carriers and conventional propulsion systems that rely on fossil fuel for its 

surface combatants and amphibious warfare ships. 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. 

You requested that we review the Navy’s assessment of alternative propulsion methods 

for submarines and surface combatants. Our objectives were to determine (1) the status 

and scope of key Navy studies on alternative propulsion methods, (2) the major 

improvements to existing propulsion systems, (3) near-term and future ships’ propulsion 

systems, and (4) the various ship propulsion related technologies the Navy is pursuing. 

In March 2006, we provided you with a briefing of our findings regarding propulsion 

systems for Navy ships and submarines. This report summarizes the results of that 

briefing as well as additional work we performed since that time, and transmits the 

briefing slides with the updated information. (See enc.) Because of command changes 

at both the Naval Sea Systems Command and the Office of the Chief of Naval Operations 

and other factors, the Navy has not completed two ongoing studies. As a result, we were 

not able to assess the results of these studies. 

To determine the status and scope of the Navy studies on alternative propulsion 

methods, the major improvements to existing propulsion systems, and the various ship 

propulsion-related technologies the Navy is pursuing, we reviewed and analyzed Navy 

and outside research organizations’ analyses and our prior report related to propulsion 

systems for Navy ships and submarines. We also discussed propulsion systems with 

officials from the Naval Sea Systems Command, the Office of Naval Research, the Office 

of Naval Reactors, the Office of the Chief of Naval Operations Surface Warfare 

GAO-06-789R Navy Propulsion Systems 
Directorate, and the Defense Advanced Research Projects Agency. We obtained and 

analyzed information on Navy propulsion technologies from officials from the Naval Sea 

Systems Command, the Office of Naval Reactors, the Office of Naval Research, and the 

Office of the Chief of Naval Operations Surface Warfare Directorate. We performed our 

work from December 2005 through April 2006 in accordance with generally accepted 

government auditing standards. 

Summary 

The Navy has completed one study, and is in the process of completing two other studies 

on alternative propulsion systems for surface combatants, amphibious warfare ships, 

and submarines. The completed study is a “quick look” analysis of comparative life cycle 

costs of nuclear and fossil-fueled surface combatants and amphibious warfare ships. 

Although the study attempted to examine the fiscal break-even point for nuclear and 

conventional propulsion systems, it had several limitations. Specifically, it did not 

consider the operational requirements or advantages of nuclear and conventionally 

powered propulsion systems, nor did it undergo a high-level, Navy-wide review. 

According to Navy officials, the second study, required by the 2005 Chief of Naval 

Operations guidance, will be similar, but will provide in-depth analysis covering costs 

and operational factors for surface combatants as well as submarines. The Navy 

anticipates that the third study, required by the National Defense Authorization Act for 

Fiscal Year 2006,1

 will build upon the Chief of Naval Operations study. Our limited 

review indicates that while the planned methodology for this study, as described by Navy

officials, appears reasonable, its usefulness will depend on the extent to which the Navy 

uses accurate, reliable data and reasonable assumptions for its modeling and considers 

all relative costs. 

Nuclear and conventional propulsion systems for Navy ships and submarines have been 

improved in recent years. According to Navy officials, nuclear power plants are now 

simpler and smaller with reduced maintenance and personnel requirements, and their 

life span has also been increased. These reported improvements have eliminated the 

need for refueling newer submarines, such as the Virginia class submarines. 

Improvements have also been reportedly made to conventional propulsion systems, such 

as the Integrated Power System, which produces electrical power for both the 

propulsion system and ship’s support systems. 

Ships being developed in the near term and long term will have a variety of newly 

designed propulsion systems depending on their size, mission, and ship characteristics. 

For example, the Littoral Combat Ship will have two diesel engines for low-speed 

operations, which will be augmented by two gas turbine engines for high-speed 

operations. The next-generation destroyer, DDG 1000,2

 will have an Integrated Power 

System consisting of four gas turbines and two advanced induction motors, which will 

supply electrical power for the propulsion and ship support systems. The first aircraft 

carrier to be built under the CVN 21 program will have a newly designed nuclear power 

 1

 Pub. L. No. 109-163, § 130 (2006). 2

 Previously referred to as DD(X).

2 GAO-06-789R Navy Propulsion Systems 
plant, and the Navy’s amphibious replacement ship, LHA 6, will utilize a combined gas 

turbine and electric propulsion system instead of the steam propulsion systems now 

used in many amphibious warfare ships. 

The Navy spent over $212 million from fiscal years 2003 through 2005, and plans to invest 

an additional $264 million from fiscal years 2006 through 2011 to develop propulsion and 

ship support technologies designed to make future ships more fuel efficient and mission 

effective. These technologies, which are at various levels of maturity and not yet ready 

for implementation, focus on making electric motors smaller but more powerful, using 

high-speed generators without reduction gears, and using fuel cells. These technologies 

will still require fossil fuel as an energy source, but Navy officials stated they have the 

potential to reduce the amount of fossil fuel needed and improve ship operations. 

Navy Has Completed One Study on Alternative Propulsion Systems and Has Two 

Others in Progress 

The Navy has completed one study and is in the process of completing two other studies 

of alternative propulsion methods for surface combatants, amphibious warfare ships, 

and submarines. These studies are (1) the 2005 “quick look” analysis of comparative 

costs of nuclear and fossil-fueled surface ships, (2) the 2005 Chief of Naval Operations 

guidance-directed study on alternative propulsion methods for surface combatants and 

submarines, and (3) the National Defense Authorization Act for Fiscal Year 2006-directed 

study on alternative propulsion methods for surface combatants and amphibious warfare 

ships. 

In the first study, the Office of Naval Reactors, which is responsible for all aspects of the 

Navy’s nuclear propulsion program and plants, conducted a “quick look” analysis of 

comparative costs of nuclear and fossil-fueled surface ships in 2005. The study 

attempted to determine the fossil fuel price point at which it becomes advantageous to 

use nuclear propulsion for amphibious warfare ships and surface combatants. This 

analysis was based on a review of historical and projected fossil fuel costs as well as the 

historical costs associated with nuclear aircraft carriers and cruisers. However, Navy 

officials cautioned that the study did not undergo a high-level Navy-wide review and 

contained several limitations and assumptions. For example, the study did not consider 

such factors as the operational advantages of nuclear and conventionally powered 

propulsion systems, the mission requirements under its Sea Power 213

 concept of 

operations, and costs associated with lead ship design. The “quick-look” analysis 

indicated that the breakeven points for a notional large deck amphibious warfare ship 

(LHA/LHD) and a notional surface combatant are $80 and $205, per barrel respectively. 

However, since this analysis contained several limitations and assumptions, a more 

comprehensive analysis may yield different results. 

 3

Sea Power 21 is the Navy’s vision of how it will organize, integrate, and transform its forces to perform 

missions in the 21st century. Its pillars are (1) Sea Strike, which is projecting precise and persistent 

offensive power; (2) Sea Shield, which is projecting global defensive assurance; and (3) Sea Basing, which 

is projecting joint operational independence. Its ForceNet concept integrates the three pillars. 

3 GAO-06-789R Navy Propulsion Systems 
In addition to the “quick look” analysis, the 2005 Chief of Naval Operations guidance 

directed the Naval Sea Systems Command to conduct a study on alternative propulsion 

methods for submarines and surface combatants. The objective of the 2005 Chief of 

Naval Operations-directed study is to evaluate current propulsion systems, considering 

the operational needs of Sea Power 21 and the cost and availability of technology and 

energy sources. The 2005 Chief of Naval Operations guidance directed the Naval Sea 

Systems Command to complete this study by July 2005; however, at the time of our 

review, Naval Sea Systems Command officials stated that because of command changes

at both the Naval Sea Systems Command and the Office of the Chief of Naval Operations, 

the study would not be completed until May 2006.4

 According to Navy officials, the Chief 

of Naval Operations-directed study will use a more comprehensive model to evaluate 

fuel source and propulsion plant alternatives for both submarines and surface 

combatants than did the “quick look” study. It will analyze ship design, using such 

factors as mission requirements; operational and support costs; manpower requirements; 

and fuel consumption, costs, and sources to determine at what price level the cost of 

diesel fuel (over the life of the ship) equals the additional life cycle cost of a similar ship 

powered by a nuclear propulsion plant. 

The National Defense Authorization Act for Fiscal Year 2006 directed the Navy to 

conduct an analysis and report on alternative propulsion methods for amphibious 

warfare ships and surface combatants by November 1, 2006. Additionally, the conferees 

directed the Navy to brief the congressional defense committees on the organization and 

study plan for the preparation of the report by April 1, 2006.5

 On April 6, 2006, the 

Subcommittee on Projection Forces, House Committee on Armed Services, held a 

hearing at which the Navy testified on its plans to conduct the study in order to fulfill the

requirement for a briefing. Navy officials stated that study guides will be developed for 

the National Defense Authorization Act study, and the study will build upon the 

methodology and results of the 2005 Chief of Naval Operations-directed study. 

Specifically, the study will analyze alternative propulsion systems in amphibious warfare 

ships, medium surface combatants, and small surface combatants; evaluate cost versus 

operational effectiveness; and compare nuclear plant with diesel fuel marine6

 plant 

alternatives. According to Navy officials, the study will analyze conceptual ship design 

to estimate acquisition costs and the life cycle costs of each variant. For each ship type, 

a break-even cost analysis will be performed to determine the cost of crude oil for which 

the life cycle cost of a nuclear propulsion variant of a ship concept will equal the life 

cycle cost of a diesel fuel marine concept. Navy officials said that the study will consider 

technologies such as nuclear power, gas turbines, diesels, fuel cells, mechanical drive, 

electrical drive, and various types of propellers, as well as other innovative concepts. 

Based on our limited analysis, the Navy’s plans to conduct the National Defense 

Authorization Act for Fiscal Year 2006-directed study, as outlined in the Navy’s statement 

for the hearing before the Subcommittee on Projection Forces, House Committee on 

 4

 On June 14, 2006, the study had not been approved by senior Navy officials. 5

 H.R. Conf. Rep. 109-360 (2005). 6

 Diesel fuel marine is a type of military fuel that is a complex mixture of hydrocarbons produced by 

distillation of crude oil. The cost of diesel fuel marine is approximately 15 percent greater than that of 

crude oil. 

4 GAO-06-789R Navy Propulsion Systems 
Armed Services, appear reasonable for conducting a more thorough analysis on 

alternative propulsion systems for surface combatants and amphibious warfare ships. 

The methodology indicates that study guides will be developed to guide the study and 

major assumptions will be identified and documented. Additionally, the methodology 

will include consideration of nuclear and fossil fuel power plants that will meet mission 

requirements, and the use of modeling techniques to capture appropriate costs and 

evaluate mission effectiveness of various propulsion plant alternatives. 

However, because the Navy had not completed its study guides for the analysis at the 

time of our review, we could not independently verify that they will be adequate to guide 

the study, nor could we determine if all relative costs will be considered and other 

pertinent factors addressed. For example, while the methodology indicated that 

manpower costs will be considered, it did not indicate whether these costs will include 

the additional training costs for nuclear-qualified personnel. Our prior work on the costeffectiveness of conventionally and nuclear-powered carriers indicated that personnel 

training costs are substantially higher for nuclear-qualified personnel.7

 Our prior work 

also documented that the support activities required for nuclear-powered ships add 

significant costs. Additionally, it is highly important that accurate, reliable data are used 

for all of the models used to support the study. The consideration of all relative costs 

and use of accurate, reliable data will determine the extent to which the study results 

will be valid and useful. 

Improvements Have Been Made to Conventional and Nuclear Propulsion 

Systems 

The Navy has made improvements to both its nuclear and conventional propulsion 

systems. According to Navy officials, nuclear power plants are now simpler in design 

and smaller; have reduced maintenance requirements; and require half the manpower of 

older plants, as demonstrated by the design of the CVN 21 class aircraft carrier. Officials 

also stated that the life of nuclear reactor cores has been extended. For example, 

according to Navy officials, the extended life span of reactor cores eliminates the need 

for refueling newer submarines, which have a 33-year life span. This compares with the 

earlier Los Angeles class submarines, which are usually refueled at the 18- to 20-year 

point in their service life. 

Improvements have also been made to conventional propulsion systems. Currently, 

conventionally powered ships have separate systems dedicated to propulsion and ship 

support systems. An improvement upon this is the Integrated Power System. According 

to Navy officials, the Integrated Power System will enable conventional systems to 

produce electrical power for both the propulsion system and ship’s support systems. 

Instead of the propeller drive shaft being connected to the engine through reduction 

gears, the Integrated Power System enables the propeller to be connected directly to an 

electric motor without the use of reduction gears. Officials further stated that the 

 7

 GAO, Navy Aircraft Carriers: Cost-Effectiveness of Conventionally and Nuclear-Powered Carriers, 

GAO/NSIAD-98-1 (Washington, D.C.: Aug. 27, 1998). 

5 GAO-06-789R Navy Propulsion Systems 
Integrated Power System will provide the electrical power for transformational weapons 

systems on future ships, improve survivability by allowing rapid reconfiguration of 

Power, and reduce acoustic signature or detection by sonar. The design of the 

Integrated Power System will require fewer components to the system, which, according 

to Navy officials, will result in reduced maintenance requirements and life cycle costs. 

Navy Ships in Development Will Have a Variety of Newly Designed Propulsion 

Systems 

Navy officials stated that ship requirement factors, which are developed during the early 

phases of ship design, drive the type of propulsion system that is selected for a ship. 

Some factors that influence the type of propulsion system selected are the maximum 

sustained speed required, operating profile (a characterization of how the ship will be 

used), acquisition cost constraints, industrial base capabilities, and the maturity of any 

new technology being considered. 

The ships planned for both near-term and future ship construction will utilize a variety of 

newly designed propulsion systems. Navy officials said that a new underway 

replenishment vessel, the T-AKE, will utilize a diesel-electric propulsion system. 

Delivery of the first T-AKE ship is expected in June 2006. Another type of ship, the 

Littoral Combat Ship, is expected to have a hybrid propulsion system consisting of two 

gas turbines, for high-speed use, and two diesel engines, for low-speed use. According to 

Navy officials, the hybrid system of the Littoral Combat Ship will enable efficient lowspeed cruising. Delivery of the first Littoral Combat Ship is expected in fiscal year 2007. 

Additional future ship construction includes a next-generation destroyer, DDG 1000; an 

amphibious replacement ship, LHA 6; a new CVN 21 class aircraft carrier; and a nextgeneration cruiser, CG(X). According to Navy officials, DDG 1000 will have an 

Integrated Power System consisting of four gas turbines and two advanced induction 

motors. The amphibious replacement ship, LHA 6, will utilize a combined gas turbine 

and electric propulsion system instead of the steam propulsion systems used in many 

amphibious warfare ships. Delivery for both DDG 1000 and LHA 6 is expected in fiscal 

year 2012. According to Navy officials, the first aircraft carrier to be built under the CVN 

21 program, CVN 78, will have a newly designed nuclear power plant, allowing for a 

reduction in both manning and reactor plant components. Delivery of CVN 78 is 

expected in fiscal year 2015. A propulsion decision has not yet been made for CG(X), 

although, according to Navy officials, CG(X) is likely to leverage the technology used in 

the DDG 1000 propulsion system, such as the Integrated Power System. 

Navy Is Spending Some Research and Development Funds to Develop New 

Propulsion Technologies 

In addition to analyzing alternative propulsion technologies for ships currently in 

development, the Navy is also spending research and development funds to develop new 

technologies to improve propulsion and support systems. For fiscal years 2003 through 

2005, the Navy spent over $212 million and plans to spend an additional $264 million for 

fiscal years 2006 through 2011 to conduct research for various technologies, such as 

6 GAO-06-789R Navy Propulsion Systems 
superconducting motors, fuel cells, and high-speed generators. None of these 

technologies are immediately ready to be implemented in ship designs. However, the 

Office of Naval Research, which is responsible for managing advanced research, has 

categorized the maturity of each technology being funded by technology readiness levels 

1 through 9. For example, a technology readiness level 1 indicates that the technology is 

still in a basic research phase, while a technology readiness level 9 indicates that a 

technology has been fully demonstrated. Some technologies being explored by the Navy, 

including fuel cell technology, high-speed generators, and superconducting motors, are 

at technology readiness levels 3 through 5. Level 5 indicates that the technologies have 

advanced to the point where stand-alone experiments can be conducted or the 

technology can be integrated with other systems in the target environment. These 

technologies will still require fossil fuel as an energy source, but Navy officials stated 

that when and if they are implemented, they will significantly reduce the amount of fuel 

required and improve ship operations. 

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. 

Agency Comments

We received technical comments from DOD, which we incorporated as appropriate. 

 __ __ __ __ 

We are sending copies of this report to the Secretary of Defense and other interested 

parties. We will provide copies of this report to others upon request. In addition, the 

report is available at no charge on the GAO Web site at http://www.gao.gov. 

7 GAO-06-789R Navy Propulsion Systems 
If you or your staff have any questions about this report, please contact me at (202) 512-

4402 or stlaurentj@gao.gov. Contact points for our Offices of Congressional Relations 

and Public Affairs may be found on the last page of this report. Key contributors to this 

report were Patricia Lentini, Assistant Director, Willie Cheely, Elisha Matvay, and George

Morse. 

Sincerely yours, 

Janet A. St. Laurent 

Director, Defense Capabilities and Management 

Enclosure 

8 GAO-06-789R Navy Propulsion Systems 
Enclosure: Status of Navy Analysis of Alternative Propulsion Systems 

9 GAO-06-789R Navy Propulsion Systems 
Enclosure: Status of Navy Analysis of Alternative Propulsion Systems 

10 GAO-06-789R Navy Propulsion Systems 
Enclosure: Status of Navy Analysis of Alternative Propulsion Systems 

11 GAO-06-789R Navy Propulsion Systems 
Enclosure: Status of Navy Analysis of Alternative Propulsion Systems 

12 GAO-06-789R Navy Propulsion Systems 
Enclosure: Status of Navy Analysis of Alternative Propulsion Systems 

13 GAO-06-789R Navy Propulsion Systems 
Enclosure: Status of Navy Analysis of Alternative Propulsion Systems 

14 GAO-06-789R Navy Propulsion Systems 
Enclosure: Status of Navy Analysis of Alternative Propulsion Systems 

15 GAO-06-789R Navy Propulsion Systems 
Enclosure: Status of Navy Analysis of Alternative Propulsion Systems 

16 GAO-06-789R Navy Propulsion Systems 
Enclosure: Status of Navy Analysis of Alternative Propulsion Systems 

(350779) 

17 GAO-06-789R Navy Propulsion Systems 
GAO’s Mission The Government Accountability Office, the audit, evaluation and 

investigative arm of Congress, exists to support Congress in meeting its 

constitutional responsibilities and to help improve the performance and 

accountability of the federal government for the American people. GAO 

examines the use of public funds; evaluates federal programs and policies; 

and provides analyses, recommendations, and other assistance to help

Congress make informed oversight, policy, and funding decisions. GAO’s 

commitment to good government is reflected in its core values of 

accountability, integrity, and reliability. 

The fastest and easiest way to obtain copies of GAO documents at no cost

is through GAO’s Web site (www.gao.gov). Each weekday, GAO posts 

newly released reports, testimony, and correspondence on its Web site. To

have GAO e-mail you a list of newly posted products every afternoon, go 

to www.gao.gov and select “Subscribe to Updates.” 

The first copy of each printed report is free. Additional copies are $2 each. 

A check or money order should be made out to the Superintendent of 

Documents. GAO also accepts VISA and Mastercard. Orders for 100 or 

more copies mailed to a single address are discounted 25 percent. Orders 

should be sent to: 

U.S. Government Accountability Office 

441 G Street NW, Room LM 

Washington, D.C. 20548 

To order by Phone: Voice: (202) 512-6000 

TDD: (202) 512-2537 

Fax: (202) 512-6061 

Contact: 

Web site: www.gao.gov/fraudnet/fraudnet.htm

E-mail: fraudnet@gao.gov

Automated answering system: (800) 424-5454 or (202) 512-7470 

Gloria Jarmon, Managing Director, JarmonG@gao.gov (202) 512-4400 

U.S. Government Accountability Office, 441 G Street NW, Room 7125 

Washington, D.C. 20548 

Paul Anderson, Managing Director, AndersonP1@gao.gov (202) 512-4800

U.S. Government Accountability Office, 441 G Street NW, Room 7149 

Washington, D.C. 20548 

Obtaining Copies of 

GAO Reports and 

Testimony

Order by Mail or Phone 

To Report Fraud,

Waste, and Abuse in 

Federal Programs 

Congressional 

Relations 

Public Affairs 

PRINTED ON RECYCLED PAPER
This is a work of the U.S. government and is not subject to copyright protection in the 

United States. It may be reproduced and distributed in its entirety without further 

permission from GAO. However, because this work may contain copyrighted images or 

other material, permission from the copyright holder may be necessary if you wish to 

reproduce this material separately.