U.S. combat operations against Iran cost about $38 billion through Aug. 1, while the campaign consumed between one-half and two-thirds of the combined U.S. inventory of four major missile-defense interceptor systems, according to a Congressional Budget Office analysis reported by Defense News. CBO estimated that rebuilding those interceptor stocks could take at least five years, even if production rates increase.

The depletion estimate covers Patriot, Terminal High Altitude Area Defense, or THAAD, Standard Missile-3 and Standard Missile-6 interceptors. The estimate applies to the combined inventory of those systems rather than to each weapon type individually. The Pentagon does not disclose the number of interceptors in its inventory, so CBO compared reported expenditures with the total number of missiles the Defense Department has purchased.

CBO said the Pentagon did not respond to its requests for information, requiring analysts to use government databases and public reports. The agency cautioned that its estimate is therefore subject to considerable uncertainty.

The interceptor expenditure represented the largest portion of the campaign’s estimated munitions replacement bill. CBO calculated that replacing munitions expended through Aug. 1 would cost $21.7 billion. Interceptors accounted for $13.1 billion of that total. Land-attack cruise missiles accounted for another $7.3 billion, while other munitions accounted for $1.2 billion.

The four interceptor systems carry high unit costs. CBO estimated a rough cost of $4 million for a Patriot or SM-6 interceptor, $12 million for a THAAD interceptor and $28 million for a sophisticated SM-3. The agency said the United States had already used significant quantities of the weapons while defending Israel before expending more during Operation Epic Fury.

CBO attributed the large early expenditure of munitions to the first few weeks of the campaign, when U.S. forces defended against Iranian ballistic-missile and drone attacks. The cost estimate includes expended munitions, equipment losses, increased flying hours, other operations and higher fuel costs. It excludes costs borne by other federal agencies and military operating costs already included in the federal budget.

Beyond munitions, the largest categories were $10.4 billion for increased flying hours, $2.7 billion for fuel and $1.9 billion to replace equipment lost in battle. The equipment losses included a THAAD radar destroyed by Iran, the analysis said.

The initial phase of Operation Epic Fury involved about 250 tactical aircraft, including roughly 90 aircraft from two carrier strike groups, along with an amphibious ready group. Bombers, airlifters, refueling tankers, other Navy vessels and Army air-defense, aviation and artillery units supported those forces.

The $38 billion CBO estimate is higher than a separate Defense Department inspector general estimate of $33.4 billion through June 29. The two figures cover different periods, and the CBO estimate includes costs through Aug. 1. CBO’s figure also reflects the categories identified in its analysis, including munitions, equipment losses, flying hours, fuel and other operations.

The administration requested $87.6 billion in supplemental funding in June. That request included $67.1 billion for the Defense Department, with $42.3 billion identified as directly related to the conflict. The directly related portion was about 10% higher than CBO’s estimate.

CBO estimated that each additional month of fighting would cost roughly $2 billion to $3 billion if the conflict continued at a relatively low intensity. Costs could be higher if operations intensified. The estimate therefore describes a campaign whose total cost can continue to rise beyond the $38 billion recorded through Aug. 1.

The interceptor drawdown creates a separate readiness problem from the dollar cost of the operation. Fewer weapons remain available for a future conflict, while replacing them could take at least five years even with higher production rates. CBO identified a conflict with China as a particular concern because Beijing maintains large numbers of ballistic and cruise missiles.