CONGRESS OF THE UNITED STATES

CONGRESSIONAL BUDGET OFFICE

A

R E P O R T

MAY 2010

Strategies for 

Maintaining the Navy’s 

and Marine Corps’ 

Inventories of

Fighter Aircraft

CBO
Pub. No. 4113
The Congress of the United States O Congressional Budget Office

A

REPORT

CBO

Strategies for Maintaining the Navy’s and 

Marine Corps’ Inventories of 

Fighter Aircraft

May 2010
CBO

Notes

All costs are in fiscal year 2010 dollars.

The cover photograph shows an F/A-18C Hornet from the “Death Rattlers” of Marine 

Strike Fighter Squadron 323 as it prepares to take off from the Nimitz-class aircraft carrier 

USS John C. Stennis. The photograph, provided courtesy of the U.S. Navy, was taken by 

Mass Communication Specialist 2nd Class Christopher Dollar.
Preface

CBO

The United States Navy and Marine Corps operate a fleet of tactical fighter aircraft that 

provide air-to-air and air-to-ground combat capabilities. Although current procurement plans 

call for the purchase of about 700 new fighter aircraft over the next 15 years, the Department 

of the Navy is projecting that purchases planned for the next 5 to 10 years will be unable to 

keep pace with the retirement of today’s F/A-18A-D Hornets as they reach the limit of their 

service life. 

This Congressional Budget Office (CBO) report—prepared as directed by the House Armed 

Services Committee’s Report on the National Defense Authorization Act for Fiscal Year 2010 

(H. Rept. 111-166)—compares several alternatives for maintaining the Navy’s and Marine 

Corps’ fighter inventory levels. The alternatives include different combinations of extending 

the service life of Hornets and purchasing new aircraft in addition to those already planned. 

In keeping with CBO’s mandate to provide objective, impartial analysis, this report makes no 

recommendations.

David Arthur of CBO’s National Security Division prepared the report under the supervision 

of Matthew Goldberg. David Newman of CBO’s Budget Analysis Division reviewed the cost 

estimates under the supervision of Sarah Jennings.

Christine Bogusz edited the report, and Loretta Lettner proofread it. Jeanine Rees prepared 

the report for publication, and Maureen Costantino designed the cover. Lenny Skutnik 

printed the initial copies of the report, Linda Schimmel handled the print distribution, and 

Simone Thomas prepared the electronic version for CBO’s Web site (www.cbo.gov).

Douglas W. Elmendorf 

Director

May 2010

Contents

CBO

Summary and Introduction 1

Inventory Implications of Current Plans 5

Approaches for Maintaining Inventories 7

High-Flight-Hour Program for Hornets 8

Service-Life Extension Program for Hornets 8

Additional Purchases of Super Hornets 9

Alternative Plans for Maintaining Fighter Inventories 9

Alternative 1: Extend Hornets’ Service Life with High-Flight-Hour Modifications 9

Alternative 2: Extend Hornets’ Service Life with SLEP and HFH Modifications 9

Alternative 3: Extend Hornets’ Service Life with HFH Modifications and 

Purchase More Super Hornets and Fewer JSFs 11

Alternative 4: Extend Hornets’ Service Life with HFH Modifications and 

Purchase Additional Super Hornets 11

Table

1. Alternatives for Maintaining the Navy’s and Marine Corps’ Fighter Inventories 3

Figures

1. The Navy’s and Marine Corps’ Inventories of Fighter Aircraft Under 

Alternative Plans 4

2. Base-Case Projection of the Navy’s and Marine Corps’ Inventories of 

Fighter Aircraft 6

3. Composition of the Navy’s and Marine Corps’ Fighter Forces Under 

Alternative Plans 10

4. Capabilities of the Navy’s and Marine Corps’ Fighter Fleets Under 

Alternative Plans 12

Boxes

1. Types of Fighter Aircraft Planned or in Use by the Navy and Marine Corps 2

2. Inventory Objectives 7

CBO

Strategies for Maintaining the Navy’s and 

Marine Corps’ Inventories of Fighter Aircraft

Summary and Introduction 

The United States Navy and Marine Corps maintain a 

fleet of more than 1,100 tactical fighters that provide 

capabilities for air-to-air combat and air-to-ground 

attack. As of January 2010, that force consisted of about 

640 F/A-18A/B/C/D Hornets, nearly 400 F/A-18E/F 

Super Hornets, and roughly 150 AV-8B Harriers. 

Current modernization plans call for replacing all of 

the Hornets and Harriers with about 100 more Super 

Hornets and 680 F-35B/C Joint Strike Fighters (JSFs). 

(See Box 1 for a brief description of those fighters.) 

The high usage rate of fighters in military operations over 

the past decade coupled with delays in the development 

of the JSF, however, have raised concerns within the 

Department of the Navy that its inventory of fighters will 

drop significantly below the level needed for the planned 

force structure over the next 10 to 15 years.1

 In particular, 

in the absence of modifications to their airframe structure, Hornets are now projected to reach the end of their 

service life faster than they can be replaced with JSFs. To 

mitigate potential inventory shortfalls, the department is 

investigating ways to extend the service life of its Hornets 

as well as changes it could make to how the fleet is 

organized and employed to reduce the number of aircraft 

needed for operations. The Navy could also reduce 

projected inventory shortfalls by purchasing more Super 

Hornets than current plans call for until the JSF can be 

delivered in large numbers.

At the direction of the House Committee on Armed Services, the Congressional Budget Office (CBO) examined 

the funding required for four alternative plans that might 

be adopted to reduce the projected decline in the fighter 

inventory. CBO did not construct alternatives to satisfy a 

particular inventory objective, nor did it attempt to judge 

the adequacy of a particular objective. The alternative 

plans consist of different combinations of three 

approaches:

B Extend the service life of Hornets by up to 600 flight 

hours (roughly two additional years) beyond the 

current 8,000-hour limit by modifying and inspecting 

F/A-18A-D aircraft in the high-flight-hour (HFH) 

program (comprising a series of structural repairs and 

more-frequent inspections);

B Implement a service-life extension program (SLEP) of 

more-extensive modifications, which would enable 

Hornets to reach 10,000 flight hours; and 

B Purchase more Super Hornets than current plans call 

for.

As of January 2010, the Navy had completed HFH 

modifications on about 25 Hornets, and Super Hornets 

are now in production. In contrast, research and planning 

for the Hornet SLEP is not expected to be complete until 

2014, although the Navy has indicated that it may begin 

SLEP modifications on some aircraft as early as 2012. In 

this analysis, CBO did not explore the potential of fielding other types of systems (such as unmanned aircraft) in 

lieu of fighters.2

Of the four alternatives that CBO analyzed, the first 

two are limited to extending the service life of existing 

1. The Navy and Marine Corps are the two military services within 

the Department of the Navy.

2. For a broader analysis of Navy, Marine Corps, and Air Force 

fighter inventories, see Congressional Budget Office, Alternatives 

for Modernizing U.S. Fighter Forces (May 2009).
2 STRATEGIES FOR MAINTAINING THE NAVY’S AND MARINE CORPS’ INVENTORIES OF FIGHTER AIRCRAFT

CBO

Hornets. They are generally consistent with various plans 

the Navy has proposed or is considering:

B Alternative 1: Execute the HFH program on the 509 

Hornets suitable for those modifications;

B Alternative 2: Execute the HFH program on 220 

Hornets and the more-extensive SLEP on 289 

Hornets.

The third and fourth alternatives would combine some 

service-life extensions for Hornets with changes in 

planned purchases of new aircraft:

B Alternative 3: Implement the HFH program in the 

same way that Alternative 1 would, but also increase 

purchases of Super Hornets by 126 aircraft (beyond 

the planned total of 515) and decrease purchases of 

JSFs by 93 aircraft between 2018 and 2023;

B Alternative 4: Modify 509 aircraft through the HFH 

process and purchase 126 additional Super Hornets, as 

in Alternative 3, but do not reduce purchases of JSF 

aircraft.

CBO measured the increase in inventory offered by those 

alternatives and the funding that each would require relative to a base case under which the service life of Hornets 

would not be extended and additional aircraft would not 

be purchased.3

 The costs cited in this report are those that 

would be incurred to make available a larger number of 

aircraft. They do not include the higher costs (for more 

fuel, for example) associated with operating a larger fleet 

of aircraft.

Under Alternative 1, CBO found that executing the 

HFH program on the 509 Hornets would increase the 

Navy’s and Marine Corps’ fighter inventory by an average 

of 66 aircraft over the 2011–2025 period (see Table 1). 

Relative to the cost of the base case (in which none of 

the three approaches are undertaken), the cost of 

Alternative 1 would be about $2.2 billion higher (in 

fiscal year 2010 dollars).4

 That cost corresponds to 

Box 1.

Types of Fighter Aircraft Planned or in Use by the 

Navy and Marine Corps

The Department of the Navy’s inventory of fighter 

aircraft includes Hornets, Super Hornets, and Harriers. (This analysis excludes the Navy’s tactical fighter 

aircraft that specialize in airborne electronic attack—

the EA-6B and the EA-18G.) The F/A-18A/B/C/D 

Hornet has been flown by both the Navy and Marine 

Corps since the 1980s. It can operate from air bases 

on land and aboard aircraft carriers. The F/A-18E/F 

Super Hornet is a newer and substantially larger 

version of the Hornet. In service since 2001, Super 

Hornets have greater flight range and can carry a 

larger weapons load than earlier versions of the 

F/A-18. Super Hornets incorporate today’s most 

advanced radars and avionics in a conventional 

airframe that includes certain design features to help 

the aircraft avoid detection by an enemy’s radars. The 

AV-8B Harrier is a short-takeoff vertical-landing 

aircraft primarily designed to attack ground targets. 

The Harrier has the flexibility to operate from tactical 

landing sites and amphibious ships. 

Within the next few years, the Department of the 

Navy plans to add Joint Strike Fighters to its inventory. The F-35B/C Joint Strike Fighter is in its developmental test stage and will not enter operational 

service until 2012 at the earliest. (The F-35B is a 

short-takeoff vertical-landing aircraft, and the F-35C 

is carrier-capable.) The Joint Strike Fighter will incorporate advanced avionics and radars in a stealthy 

(designed to avoid detection by radar) airframe. 

3. The base case essentially posits minimal action being taken to 

mitigate impending inventory shortfalls. CBO selected this as its 

reference case for comparing alternatives because the Department 

of the Navy’s plans remain fluid.

4. Costs for the HFH and SLEP modifications are based on estimates from the Department of the Navy. The cost of additional 

Super Hornets is based on actual costs for planned purchases 

under annual production contracts. 
STRATEGIES FOR MAINTAINING THE NAVY’S AND MARINE CORPS’ INVENTORIES OF FIGHTER AIRCRAFT 3

CBO

Table 1.

Alternatives for Maintaining the Navy’s and Marine Corps’ Fighter Inventories

Source: Congressional Budget Office.

Notes: Under the base-case scenario, Hornets would be retired from service at 8,000 flight hours.

Aircraft-years are a measure of the service provided by an aircraft. One aircraft-year is equal to one year of service from one aircraft.

The additional costs are those incurred to make available a larger number of aircraft. They do not include the higher costs (for more 

fuel, for example) associated with operating a larger fleet of aircraft.

The higher costs shown for Alternatives 3 and 4 reflect prices consistent with annual procurement contracts for Super Hornets 

purchased in addition to those currently planned. The lower costs reflect prices consistent with a proposed multiyear procurement 

contract for Super Hornets that the Department of Defense plans to award.

approximately $2.2 million per aircraft-year of additional 

service made available to the fleet.5

 Alternative 1 has the 

lowest total cost of the alternatives examined by CBO, 

but it provides the smallest increase in inventory.

Alternative 2 would provide 220 HFH Hornets plus 289 

SLEP Hornets, increasing the department’s total inventory by an average of 106 aircraft over the 2011–2025 

period, at a cost of about $7.7 billion. This alternative 

would provide the largest increase in inventory that can 

be achieved with the HFH and SLEP modifications currently being considered. At $4.8 million per aircraft-year, 

however, Alternative 2 is more than twice as costly per 

increment of additional service than is Alternative 1.

Alternative 3 is constructed to maintain an inventory of 

no less than that of Alternative 2 in any given year and to 

yield an inventory close to that of Alternatives 1 and 2 in 

2025 (by shifting purchases of new aircraft to earlier 

years, when the inventory is projected to be the lowest). 

It would increase the average inventory by 128 aircraft 

through 2025 (see Figure 1). 

Alternative 3 would provide larger increases in inventory 

than would Alternatives 1 and 2. Moreover, each additional Super Hornet provided under Alternative 3 would 

offer improved performance (a more-capable radar, longer range, and the ability to carry more weapons) than 

1234

Hornets in High-Flight-Hour Program 509 220 509 509

Hornets in Service Life Extension Program 0 289 0 0

Additional Super Hornet Purchases 0 0 126 126

Change in Joint Strike Fighter Purchases 0 0 -93 0

Average Increase in Inventory, 2011 to 2025 66 106 128 148

Increase in Inventory Above Low Point from 2011 to 2025 71 135 174 191

Between 2011 and 2025 1,000 1,600 1,900 2,200

After 2025 0 0 -100 1,700

Total, 2011 to 2015 1,100 3,700 10,300–11,300 10,300–11,300

Total, 2011 to 2025 2,200 7,700 3,800–4,800 11,600–12,600

Average per Aircraft-Year, 2011 to 2025 2.2 4.8 2.0–2.5 5.3–5.7

Average per Aircraft-Year, Lifetime 2.2 4.8 2.2–2.7 2.9–3.2

Alternatives

Cost Above the Base Case

Number of Aircraft

 (Millions of fiscal year 2010 dollars)

Additional Aircraft-Years of Service

Relative to the Base Case

5. Aircraft-years are a measure of the service provided by an aircraft. 

One aircraft-year is equal to one year of service from one aircraft.
4 STRATEGIES FOR MAINTAINING THE NAVY’S AND MARINE CORPS’ INVENTORIES OF FIGHTER AIRCRAFT

CBO

Figure 1.

The Navy’s and Marine Corps’ Inventories of Fighter Aircraft Under 

Alternative Plans

(Total aircraft inventory)

Source: Congressional Budget Office.

Notes: Under the base-case scenario, Hornets would be retired from service at 8,000 flight hours. Under Alternative 1, 509 Hornets would 

receive modifications under the high-flight-hour (HFH) program, which would extend their service life by 600 flight hours. Under 

Alternative 2, 220 Hornets would receive HFH modifications; another 289 Hornets would receive more-extensive modifications under 

the service-life extension program, which would increase their service life to 10,000 hours. Under Alternative 3, 509 Hornets would 

receive HFH modifications; also, the Department of the Navy would purchase 126 additional Super Hornets but 93 fewer Joint Strike 

Fighters (JSFs). Under Alternative 4, 509 Hornets would receive HFH modifications, and the Navy would purchase 126 additional Super 

Hornets (but not reduce the number of JSF aircraft.)

The dotted band indicates a range of inventory objectives derived from information provided by the Navy (see Box 2 for details).

Inventories are based on JSF purchase schedules as described in Department of Defense 30-Year Aviation Plan (February 2010).

would a SLEP Hornet. The reduction in JSF purchases 

would result in fewer of the most advanced aircraft after 

2020, however.

At about $3.8 billion to $4.8 billion higher than the 

cost of the base case, the total cost of Alternative 3 would 

fall between the costs of Alternatives 1 and 2.6

 The 

cost per increment of additional service—$2.0 million 

to $2.5 million per aircraft-year over the 2011–2025 

period—would be comparable to that of Alternative 1. In 

the near term, however, the cost would be substantially 

higher ($10.3 billion to $11.3 billion versus $3.7 billion 

for Alternative 2 over the 2011–2015 period, for example) because the savings from reducing JSF purchases 

would not offset the cost of new Super Hornet purchases 

until after 2017.

Under Alternative 4, the Department of the Navy would 

modify 509 Hornets and purchase 126 additional Super 

Hornets, as in Alternative 3, but would not reduce purchases of JSF aircraft. The increase in average inventory 

would be 148 aircraft between 2011 and 2025, 20 aircraft more than under Alternative 3. Alternative 4 would 

also provide increased inventory well beyond 2025, 

because additional purchases of Super Hornets would not 

be offset by fewer purchases of JSFs. (Unlike HFH and 

SLEP aircraft, which would be taken out of service by 

2025, new Super Hornets could remain in the fleet for 25 

years or longer.)

2010 2012 2014 2016 2018 2020 2022 2024 2026 2028 2030

0

200

400

600

800

1,000

1,200

1,400

Base Case

Alternative 1 Alternative 2

Alternative 3

Alternative 4

6. The upper end of the cost ranges for Alternatives 3 and 4 reflect 

F/A-18E/F purchases under annual procurement contracts at 

prices consistent with those assumed in the President’s fiscal year 

2011 budget request. The lower end of the range is based on 

prices consistent with those in a proposed multiyear procurement 

contract for F/A-18E/F aircraft that the Department of Defense 

plans to award by September 30, 2010.
STRATEGIES FOR MAINTAINING THE NAVY’S AND MARINE CORPS’ INVENTORIES OF FIGHTER AIRCRAFT 5

CBO

The advantages of new aircraft provided in Alternative 4 

would come at a cost of $12 billion to $13 billion more 

than under the base case (nearly all of which would be 

incurred in the next five years). At a cost of $5.3 million 

to $5.7 million per aircraft-year, Alternative 4 would be 

the most expensive per increment of additional service 

provided between 2011 and 2025. If the aircraft-years 

of service after 2025 are included, the cost would be 

$2.9 million to $3.2 million per aircraft-year. Super 

Hornet service after 2025 may not have the same military 

value as service between 2011 and 2025, however.

CBO did not evaluate whether the inventories that would 

be realized under the various alternatives would be sufficient to meet the Navy’s and Marine Corps’ operational 

needs. A series of briefings since 2008 from the Department of the Navy to the Congress has explicitly or 

implicitly suggested sustained inventory objectives ranging from slightly more than 1,000 aircraft to as many as 

1,240 aircraft (see the dotted band in Figure 1). None of 

the alternatives that CBO considered would provide 

inventories within that range of objectives for all years 

through 2025, although Alternatives 3 and 4 would come 

closest. 

The inventories realized under all four alternatives would 

be lower, and any corresponding shortfall would be 

larger, if further delays were experienced with the JSF 

program. Under those circumstances, a greater increase in 

Super Hornet purchases could be incorporated into any 

of the alternatives if the Super Hornet production line 

was still in operation. Compensating for further delays in 

the JSF program by keeping Hornets in the fleet longer 

than envisioned with HFH or SLEP modifications would 

require much more extensive (and, probably, much more 

costly) modifications.

Inventory Implications of 

Current Plans

As of January 2010, the Department of the Navy’s inventory of fighter aircraft included Hornets (382 in service in 

the Navy and 254 in the Marine Corps), Super Hornets 

(398 in service, all with the Navy), and Harriers (146 

in service, all with the Marine Corps).7

 Within the next 

few years, the Department of the Navy plans to add two 

versions of the Joint Strike Fighter to its inventory. The 

Navy plans to operate the carrier-capable F-35C, whereas 

the Marine Corps prefers the short-takeoff verticallanding F-35B, which can be flown from amphibious 

ships and small airfields ashore.8

Despite plans to spend an average of about $6.4 billion 

per year for new fighter aircraft over the next decade, the 

Navy projects that its fighter inventories will fall substantially as Hornets reach their service-life limit of 8,000 

flight hours and are retired in large numbers. CBO also 

anticipates that the Harriers will be retired by 2020. As a 

result, in the absence of action to extend the life of 

existing aircraft or purchase new aircraft in addition to 

those currently planned, the Navy’s and Marine Corps’ 

combined fighter inventory would drop to roughly 800 

aircraft in 2020, by CBO’s estimation—about 30 percent 

lower than today’s inventory—before rebounding 

through 2025 (see Figure 2). 

On the basis of information from the Navy, CBO’s 

projection includes a service life of 9,000 flight hours for 

Super Hornets. Although Super Hornets were designed 

for 6,000 flight hours, the Navy is confident that limit 

can be extended. (The Hornet was originally designed for 

6,000 flight hours as well, and its limit has already been 

extended to as high as 8,600 hours.)

The assumption that AV-8B Harriers will be retired by 

2020 is based on data provided by the Navy in November 

2008. However, as CBO noted in its May 2009 report 

Alternatives for Modernizing U.S. Fighter Forces, Harriers 

could be maintained in the force longer, if necessary, 

because their scheduled retirement is based on deliveries 

of F-35Bs rather than structural service-life limitations 

like those facing the Hornets. In recent testimony before 

the Congress, the Navy has indicated that it is exploring 

7. This paper does not consider tactical fighter aircraft specialized for 

airborne electronic attack—in particular, the EA-6B Prowler and 

its replacement, the EA-18G Growler—in its discussion of inventory goals.

8. The mix of F-35Bs and F-35Cs has not yet been decided. It will 

depend on the extent to which the Marines will be responsible for 

providing squadrons to augment Navy squadrons aboard aircraft 

carriers and whether F-35Bs will be suitable in that role. The 

Navy would prefer that the Marines provide squadrons equipped 

with F-35Cs, arguing that the longer range and heavier payload 

offered by the C model would be critical when flying from aircraft 

carriers that might be far out at sea and that the B model would 

require additional logistics support and equipment aboard ship. 

The Marines would prefer to operate only one type of fighter. 

Another version of the JSF, the F-35A, is being developed for the 

Air Force and does not figure into the current analysis.
6 STRATEGIES FOR MAINTAINING THE NAVY’S AND MARINE CORPS’ INVENTORIES OF FIGHTER AIRCRAFT

CBO

Figure 2.

Base-Case Projection of the Navy’s and Marine Corps’ Inventories of 

Fighter Aircraft

(Total aircraft inventory)

Source: Congressional Budget Office.

Notes: Under the base case, Hornets would be retired at 8,000 flight hours, and Harriers would be taken out of service by 2020 (as they were 

replaced by Joint Strike Fighters). The Navy has begun extending the service life of Hornets to as much as 8,600 flight hours, and it is 

investigating options for maintaining Harriers in the fleet until 2022 (or beyond).

The dotted band indicates a range of inventory objectives derived from information provided by the Navy (see Box 2 for details).

Inventories of JSFs are based on purchase schedules as described in Department of Defense 30-Year Aviation Plan (February 2010).

ways to upgrade Harriers’ capabilities and improve 

readiness, which could keep those aircraft in the force 

through at least 2022.

According to budget documents submitted by the 

Department of Defense in its fiscal year 2011 budget 

request, 48 more Super Hornets will be purchased 

through 2013, at a cost of $4.4 billion (in fiscal year 

2010 dollars), bringing total Super Hornet purchases 

to 515 aircraft.9

 (That cost could decrease by about 

$300 million under a proposed multiyear procurement 

contract that the Defense Department plans to award by 

September 30, 2010.) Over the 2011–2015 period 

detailed in the 2011 budget request, the Navy would 

purchase 98 F-35Bs and 61 F-35Cs, at a cost of nearly 

$30 billion. After 2015, according to the Department of 

Defense 30-Year Aviation Plan submitted to the Congress 

in February 2010, another 283 F-35B/C aircraft would 

be purchased through 2020, with production reaching 

66 aircraft in that year.10 Under CBO’s assumption that 

that rate of production is maintained, JSF procurement 

by the Department of the Navy would reach its planned 

total of 680 aircraft in 2023. According to estimates in 

the fiscal year 2011 budget request, procurement costs for 

F-35B/Cs would total about $78 billion (from 2011 

through the end of production).11

2010 2012 2014 2016 2018 2020 2022 2024 2026 2028 2030

0

200

400

600

800

1,000

1,200

1,400

AV-8B Harriers

F-35B/C Joint Strike Fighters

F/A-18A-D Hornets

F/A-18E/F Super Hornets

9. That total includes aircraft in the inventory, aircraft that have 

been purchased but not yet delivered, and aircraft yet to be 

purchased, deducting aircraft that have been lost in combat or 

mishaps.

10. The plan provided details of quantities to be purchased between 

2010 and 2020. 

11. Cost estimates for the JSF are based on plans outlined in the 

President’s fiscal year 2011 budget request. Near the end of March 

2010, however, the Secretary of Defense notified the Congress 

that the JSF program had breached so-called Nunn-McCurdy 

cost-growth thresholds specified in section 2433 of title 10, 

U.S. Code, and that the program will probably be subject to 

changes in its cost and procurement schedules.
STRATEGIES FOR MAINTAINING THE NAVY’S AND MARINE CORPS’ INVENTORIES OF FIGHTER AIRCRAFT 7

CBO

Approaches for Maintaining 

Inventories

The range of inventory objectives illustrated by CBO—

1,060 to 1,240 aircraft—reflects different assumptions 

about future force structures and operational demands for 

aircraft. (See Box 2 for a description of how CBO derived 

that range of values for inventory objectives.) Under 

CBO’s projection, if Hornets were retired at 8,000 flight 

hours and no new aircraft were purchased in addition to 

those currently planned, the number of fighter aircraft in 

the Navy and Marine Corps would drop below the range 

of inventory objectives after 2011 and would remain 

below that range until JSF deliveries were completed in 

about 2025.

Reducing or eliminating the gap between projected 

inventories and inventory objectives will require some 

combination of service-life extensions for existing aircraft, 

purchases of new aircraft beyond those already planned, 

or reductions in inventory objectives (either by improving efficiency through organizational and operational 

changes or by reducing the scope or number of missions 

the force will be expected to accomplish). To that end, 

the Navy is pursuing organizational changes, such as 

reductions in the number of aircraft assigned to squadrons that are not deployed. To maintain larger inventories, the Navy is carefully managing the factors that limit 

the life of each aircraft in the Hornet fleet. For example, 

aircraft on a pace to reach their limit of catapult launches 

or arrested landings before reaching their flight-hour 

limit might be transferred to a Marine Corps squadron 

operating from a land base.

This report considers three approaches that could be 

adopted to help maintain fighter inventories through 

2025. Two of those approaches would combine structural 

repairs and modifications with increased inspections to 

allow Hornets to operate beyond 8,000 flight hours. A 

Box 2.

Inventory Objectives

The Department of the Navy has most frequently 

described the future of its fighter inventory in terms 

of a projected shortfall—a measure of the difference 

between the number of aircraft desired at a specific 

point in time and a projection of what the inventory 

will actually be at that time. Less frequently stated, 

however, are the inventory goals and inventory projections that are used to calculate the shortfall values. 

In the absence of a well-established definition of 

fighter inventory goals, the Congressional Budget 

Office (CBO) compares its projections of fighter 

inventories against a range of possible inventory goals 

that can be derived from various sources.

The top end of the range is 1,240 aircraft. That value 

was identified in a February 2010 briefing by the 

department as the combined requirement for the 

Navy and Marine Corps. It includes 42 Navy squadrons and 24 Marine Corps squadrons. In that briefing, the department also quoted an “Existing 

TACAIR [Tactical Aircraft] Demand” of 1,154 aircraft that is based on current operations and includes 

37 Navy squadrons and 20 Marine Corps squadrons. 

The lower end of the range of inventory objectives, 

1,060 aircraft, corresponds to CBO’s projection of 

the Navy’s and Marine Corps’ Super Hornet and JSF 

inventory in 2025 (deducting estimated losses from 

attrition). That inventory is consistent with planned 

purchases, the retirement of the Harrier force by or 

before 2025, and the Navy’s February 2010 projection of no shortfall in 2025.

Of course, the number of aircraft actually needed to 

support a given force can vary over time as, for example, the need for backup aircraft to replace aircraft 

lost in combat or mishaps varies or as the fraction of 

time spent in depot maintenance increases as aircraft 

age. Force structure requirements can vary as well. 

For example, the period of time in the next decade 

when the Navy’s carrier force is projected to temporarily drop from 11 to 10 (between the retirement of 

the USS Enterprise and the commissioning of the 

USS Gerald R. Ford) could result in a temporarily 

reduced need for carrier aircraft. Information provided to CBO by the Navy in the past indicated that 

its objective did vary over time.
8 STRATEGIES FOR MAINTAINING THE NAVY’S AND MARINE CORPS’ INVENTORIES OF FIGHTER AIRCRAFT

CBO

third approach would increase purchases of Super Hornets. Although it might be possible to increase purchases 

of JSF aircraft in later years, that approach was not considered in this analysis because it appears unlikely that 

accelerating JSF purchases will be feasible during the 

years for which shortfalls are projected. The subsequent 

section details four alternative plans—comprised of combinations of those approaches—that would maintain 

higher Navy and Marine Corps fighter inventories 

through 2025.

This analysis does not examine the years after 2025, when 

the Navy’s fighter inventories are projected to drop again 

as the service begins to retire its Super Hornets. To 

maintain inventory levels after 2025, the Navy will need 

to extend the service life of its Super Hornets, purchase 

additional JSFs, or field a new aircraft. Fielding a new aircraft will require funding for research and development 

beginning perhaps as early as 2015 and reaching substantial amounts by 2020. Those costs are not included in 

this analysis.

High-Flight-Hour Program for Hornets

Under one approach, the high-flight-hour program for 

extending Hornets’ service life, the Navy would implement a series of structural repairs or modifications followed by an increased frequency of inspections, which 

would enable most of its Hornet aircraft to operate for up 

to 600 flight hours (roughly two additional years) beyond 

the current limit of 8,000 flight hours. Aircraft approaching 8,000 hours would be repaired and modified during 

their scheduled depot maintenance. Upon completion, 

the aircraft would be certified for 600 flight hours in 

addition to the flight hours already accrued.

On the basis of estimates provided by the Navy, CBO 

assumed that the cost for each HFH aircraft would be 

about $4.5 million, distributed over the additional life of 

the aircraft. Although the HFH program would only 

modify or repair structural components of the aircraft, 

other potentially life-limiting factors (such as engine 

service life) are not expected to prevent HFH-modified 

Hornets from realizing their extended life. Consequently, 

most Hornets in the force would be candidates for the 

HFH modifications.

Through the end of 2009, the Navy had completed HFH 

modifications on about 25 Hornets and had begun 

modifying about 25 more. Because those 50 aircraft 

had accrued an average of 7,800 flight hours when they 

entered the program, CBO’s inventory projections 

assume that HFH Hornets will achieve an average of 

8,400 flight hours. Although the HFH program could be 

considered to be part of the base-case plan, CBO treated 

it as an alternative (instead of assuming that all Hornets 

would have HFH modifications as part of the base case) 

because the number of aircraft that receive HFH modifications could be varied depending on what other actions 

are taken to maintain inventory levels.

Service-Life Extension Program for Hornets

Another approach would involve the Hornets’ service-life 

extension program: The Navy would implement moreextensive structural repairs or modifications followed by 

an increased frequency of inspections, enabling many of 

its Hornet aircraft to operate for up to 10,000 flight 

hours. On the basis of estimates provided by the Navy, 

CBO projected that the cost for each SLEP Hornet 

would be about $23 million: $13 million up front (for 

modifications) and $10 million distributed over the 

remaining life of the aircraft (for further modifications 

and inspections).12 Considerable uncertainty underlies 

that cost estimate, however, because the details of the necessary modifications and inspections have not been finalized.13 Consequently, there is a greater risk of cost growth 

with SLEP modifications than with HFH modifications.

Because the SLEP modifications would be much more 

extensive than the HFH modifications, fewer Hornets 

would be suitable for the program. In particular, aircraft 

that were likely to reach other life-limiting conditions 

before a significant portion of their additional 2,000 

flight hours could be expended would not be worth the 

up-front expense of SLEP modifications. Under the 

assumption that a SLEP Hornet should be operable for at 

least three additional years—a condition established by 

the Navy—CBO estimates that slightly fewer than 300 

Hornets would be suitable for SLEP modifications. The 

12. The funding spread over the additional service life of SLEP- and 

HFH-modified Hornets would provide for additional inspections 

and for other activities related to operating an aircraft well beyond 

its design service life.

13. The planning schedule for developing the SLEP Hornet described 

in an October 2009 briefing from the Navy indicated that a “40% 

Total SLEP Solution” could be in hand by 2012, 80 percent by 

2013, and 100 percent by 2014. On the basis of that information, 

CBO assumes that Hornets could begin undergoing SLEP modifications as early as 2012.
STRATEGIES FOR MAINTAINING THE NAVY’S AND MARINE CORPS’ INVENTORIES OF FIGHTER AIRCRAFT 9

CBO

remainder could be suitable for HFH modifications, 

however.

Additional Purchases of Super Hornets

The Navy and Marine Corps could also increase their 

fighter inventories through 2025 by purchasing additional Super Hornets. CBO’s cost estimates for the 

alternatives that include additional Super Hornets are 

presented as a range reflecting the possibility that those 

aircraft could be purchased either under annual procurement contracts or, at a lower cost, under a multiyear procurement contract. 

For costs under annual procurement contracts, CBO 

assumed that Super Hornet production could continue at 

prices similar to those described in the President’s budget 

request for fiscal year 2011 (released in February 2010). 

CBO based its cost estimates for purchases under a 

multiyear contract on the details of a proposed contract 

described in a May 2010 letter from the Defense Department to the Congress. CBO assumed that savings resulting from cost-reduction initiatives undertaken as part of a 

multiyear contract for planned Super Hornets could also 

be obtained for Super Hornets purchased in addition to 

those currently planned.

Alternative Plans for Maintaining 

Fighter Inventories

CBO examined four ways in which combinations of 

service-life extensions to existing aircraft and purchases 

of new aircraft (in addition to those currently planned) 

could mitigate the drop in fighter inventories predicted 

for the Navy and Marine Corps over the next 15 years. 

Alternatives 1 and 2 include only service-life extensions, 

whereas Alternatives 3 and 4 combine service-life extensions with purchases of new aircraft.

Alternative 1: Extend Hornets’ Service Life with 

High-Flight-Hour Modifications

Under this alternative, the Navy would subject all suitable Hornets to HFH service-life extensions. Modifications would continue through 2022, ultimately yielding 

509 HFH Hornets, at a total cost of about $2.2 billion. 

The additional aircraft would increase the inventory by 

an average of 66 aircraft over the 2011–2025 period (see 

the upper left panel in Figure 3). The inventory of HFH 

aircraft would reach a maximum of 119 aircraft in 2015.

The primary advantages of Alternative 1 are its lower cost 

relative to the other alternatives—about $2.2 million per 

aircraft-year of additional service—and the fact that its 

effects are concentrated during the years of projected 

inventory shortfalls (see Table 1). The aircraft-years of 

additional service are illustrated by the area labeled 

“HFH Hornet” in Figure 3.

The primary disadvantage of Alternative 1 is the limited 

increase in inventory that can be achieved with HFH 

modifications alone. Total inventories under Alternative 

1 would decline to fewer than 900 aircraft in 2020, CBO 

projects, about 25 percent below today’s inventory. Those 

amounts are well below the range of inventory objectives 

that CBO derived from Navy briefings. 

Alternative 2: Extend Hornets’ Service Life with 

SLEP and HFH Modifications

Under Alternative 2, the Navy would implement SLEP 

modifications on all qualified Hornets (289 aircraft) and 

conduct the more limited HFH service-life extensions on 

the remainder (220 aircraft), at a total cost of about 

$7.7 billion. Fighter inventories would increase by an 

average of 106 aircraft between 2011 and 2025 (see the 

upper right panel in Figure 3). The inventory increase 

would be highest—225 aircraft—in 2017.

As with Alternative 1, the inventory increase achieved 

under Alternative 2 would be realized during the years 

when inventories were lowest. Although Alternative 2 

would provide a larger increase in inventory than 

Alternative 1, that increase would come at a substantially 

higher cost per aircraft-year of increased inventory (about 

$4.8 million), more than double the cost per aircraft-year 

under Alternative 1. The higher cost is a result of the 

more substantial structural work needed to achieve 

10,000 flight hours plus the cost of additional inspections 

for SLEP aircraft that would remain in the force for a 

longer time.

Under Alternative 2, inventories could be maintained at 

or close to the range of inventory objectives through 

about 2018. Inventories would then drop somewhat 

before climbing again after 2023, when JSF deliveries 

would begin to outpace retirements of old aircraft.

Alternative 2 is similar to a Navy proposal that would 

include 206 HFH and 280 SLEP Hornets. The Navy is 

also examining plans that would extend the service life
10 STRATEGIES FOR MAINTAINING THE NAVY’S AND MARINE CORPS’ INVENTORIES OF FIGHTER AIRCRAFT

CBO

Figure 3.

Composition of the Navy’s and Marine Corps’ Fighter Forces Under 

Alternative Plans 

(Total aircraft inventory)

Source: Congressional Budget Office.

Notes: Under the base-case scenario (not shown), Hornets (F/A-18A-D) would be retired from service at 8,000 flight hours, and Harriers 

(AV-8B) would be taken out of service by 2020 as they were replaced by Joint Strike Fighters (JSFs). Under Alternative 1, 

509 Hornets would receive modifications under the high-flight-hour (HFH) program, which would extend their service life by 

600 flight hours. Under Alternative 2, 220 Hornets would receive HFH modifications; another 289 Hornets would receive moreextensive modifications under the service-life extension program (SLEP), which would increase their service life to 10,000 hours. 

Under Alternative 3, 509 Hornets would receive HFH modifications; also, the Department of the Navy would purchase 126 additional 

Super Hornets (F/A-18E/F) but 93 fewer Joint Strike Fighters (F-35B/C). Under Alternative 4, 509 Hornets would receive HFH modifications, and the Navy would purchase 126 additional Super Hornets (but not reduce the number of JSFs).

The dotted band indicates a range of inventory objectives derived from information provided by the Navy (see Box 2 for details).

Inventories of JSFs are based on purchase schedules as described in Department of Defense 30-Year Aviation Plan (February 2010).

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STRATEGIES FOR MAINTAINING THE NAVY’S AND MARINE CORPS’ INVENTORIES OF FIGHTER AIRCRAFT 11

CBO

of fewer Hornets. In particular, the Navy has cited a proposal that would add SLEP modifications to150 Hornets. 

By modifying a smaller number of aircraft, the Navy 

would be able to reduce its costs and have greater flexibility to select for modification only aircraft that were in the 

best condition. Fewer aircraft would be made available to 

the force in that case, however.

Alternative 3: Extend Hornets’ Service Life with HFH 

Modifications and Purchase More Super Hornets 

and Fewer JSFs

Under Alternative 3, the Navy would purchase 126 additional Super Hornets over the next several years, when the 

fighter inventory is projected to be at its lowest, and partially offset those additional aircraft by decreasing its purchases of Joint Strike Fighters by 93 aircraft in later years. 

This alternative would yield an inventory that was equal 

to or greater than that of Alternative 2 in each year and 

slightly greater than the base case (and Alternatives 1 

and 2) in 2025 (see the lower left panel inFigure 3).14 The 

total cost of Alternative 3 would be $3.8 billion 

to $4.8 billion more than the base case (under multiyear 

and annual procurement contracts, respectively) and 

would be between the costs of the first two alternatives. 

However, the cost would be disproportionately shifted to 

earlier years: Alternative 3 would cost about $10.3 billion 

to $11.3 billion more than the base case over the 2011–

2015 period and then $6.5 billion less than the base case 

from 2016 to 2023.

The 126 additional Super Hornets would be purchased 

through 2015. (Specifically, 8 would be purchased in 

2011, 17 each in 2012 and 2013, and 42 each in 2014 

and 2015.) That pace would result in a steady production 

rate of 42 aircraft per year when it was combined with 

planned purchases of F/A-18E/Fs and EA-18Gs.15

Reductions in JSF purchases would be made between 

2018 and 2023. Purchases of B- and C-model JSFs 

would be capped at 50 aircraft per year between 2018 

and 2023 instead of the rate of more than 65 aircraft per 

year that was indicated in the Department of Defense 30-

Year Aviation Plan. CBO did not assume specific reductions in quantities of B- and C-model JSFs because the 

Navy and Marine Corps have not yet specified what the 

B/C mix will be for the 680 JSFs they plan to purchase.

The additional aircraft purchased in earlier years would 

result in an average increase in inventory of about 128 

aircraft between 2011 and 2025. The total inventory 

would be maintained at close to or well above 1,000 

aircraft over that period. In addition, each Super Hornet 

purchased under Alternative 3 would be more capable 

than the Hornet it replaced, shifting the aggregate technological capability of the fleet upward (see Figure 4). By 

2020, for example, the fleet under Alternative 3 would 

include almost 20 percent more aircraft equipped with 

active electronically scanned array radars than the force 

under Alternatives 1 and 2 would have. The force under 

Alternative 3 would have fewer stealthy aircraft after 

2020, however.

Alternative 3 also would present a lesser technical and 

cost risk than Alternative 2 because it would involve 

purchasing the proven Super Hornet in lieu of SLEP 

Hornets, for which modifications and inspection 

schedules have yet to be finalized. Additionally, keeping 

Super Hornet production open for several more years 

could provide a hedge against further development or 

production problems that might arise for the JSF.

Alternative 4: Extend Hornets’ Service Life with HFH 

Modifications and Purchase Additional Super 

Hornets

Under Alternative 4, the Navy would modify 509 Hornets under the high-flight-hour program and purchase an 

additional 126 Super Hornets, but it would not decrease 

its JSF purchases. As a result, fighter inventories would be 

greater than or equal to those of Alternative 2 in each year 14. The inventory in 2025 under Alternative 3 would be about 40 aircraft higher than under Alternatives 1 and 2. A larger reduction in 

procurement of F-35B/Cs could have yielded a closer match, but 

it would introduce the potential of substantial changes in unit cost 

resulting from a lower rate of production. A detailed estimate of 

that effect was not possible because the number of F-35Bs versus 

F-35Cs has not been established. Consequently, CBO assumed a 

rate of 50 F-35B/Cs per year (the same rate as was used in earlier 

plans from the Department of the Navy) as a floor for F-35B/C 

procurement.

15. The additional Super Hornets in 2011, 2012, and 2013 could be 

purchased under the multiyear contract that the Department of 

Defense is considering for the remaining planned Super Hornets 

(and Growlers) because the proposed contract would allow the 

Defense Department to increase purchases up to a maximum of 

54 aircraft per year. Those terms could change before the contract 

is awarded, however.
12 STRATEGIES FOR MAINTAINING THE NAVY’S AND MARINE CORPS’ INVENTORIES OF FIGHTER AIRCRAFT

CBO

Figure 4.

Capabilities of the Navy’s and Marine Corps’ Fighter Fleets Under 

Alternative Plans 

(Total aircraft inventory)

Source: Congressional Budget Office.

Notes: Under the base-case scenario, Hornets would be retired from service at 8,000 flight hours. Under Alternative 1, 509 Hornets would 

receive modifications under the high-flight-hour (HFH) program, which would extend their service life by 600 flight hours. Under 

Alternative 2, 220 Hornets would receive HFH modifications; another 289 Hornets would receive more-extensive modifications 

under the service-life extension program, which would increase their service life to 10,000 hours. Under Alternative 3, 509 Hornets 

would receive HFH modifications; also, the Department of the Navy would purchase 126 additional Super Hornets but 93 fewer Joint 

Strike Fighters (JSFs). Under Alternative 4, 509 Hornets would receive HFH modifications, and the Navy would purchase 126 additional 

Super Hornets (but not reduce the number of JSF aircraft.)

The “conventional” category includes F/A-18A-D Hornets and the earliest production (Block 1) F/A-18E/F Super Hornets, which 

are not equipped with active electronically scanned array (AESA) radars. The “AESA” category includes the remaining (Block 2) 

Super Hornets, which are equipped with AESA radars. The “stealth” category includes F-35B/C Joint Strike Fighters (which also carry 

AESA radars). 

Inventories of JSFs are based on purchase schedules as described in Department of Defense 30-Year Aviation Plan (February 2010).

and significantly larger after 2018 (see the lower right 

panel in Figure 3). Over the 2011–2025 period, the average inventory would increase by 148 aircraft and would 

remain above 1,000 aircraft. Alternative 4 would have the 

highest cost of the alternatives that CBO examined—

about $11.6 billion to $12.6 billion more than the base 

case. As with Alternative 3, nearly all of that additional 

cost would occur over the next five years.

The improvements that would be realized under Alternative 4 would come at a cost per aircraft-year of inventory 

of about $5.3 million to $5.7 million from 2011 to 2025, 

an amount higher than the cost of the other three alternatives considered by CBO. However, if the 1,700 aircraftyears of inventory provided after 2025 are included, the 

cost would be $2.9 million to $3.2 million per aircraftyear purchased, which is between the costs of Alternative 

1 and Alternative 2. It is not clear, however, whether an 

aircraft-year of inventory after 2025 would be of equal 

operational value to one before 2025 because inventory 

demands may be different and other, more advanced, 

aircraft may be beginning to enter the force at that time. 

Nevertheless, the additional inventory that would be 

provided after 2025 could serve as a hedge against a 

future need to increase force structure or against delays in 

whatever system the Navy might pursue to replace the 

Super Hornet.

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