CSIS ‘Last Rounds’: Half of Prewar Inventory Expended on Four US Munitions in Iran War

Intelligence Summary

The Center for Strategic and International Studies (CSIS) has published “Last Rounds? Status of Key Munitions at the Iran War Ceasefire,” the first credible open-source quantification of US precision munition expenditure across the 39-day air-and-missile campaign. The assessment covers seven key munitions across two operational categories: long-range land-attack and air-and-missile defence (AMD) interceptors. CSIS concludes that the United States may have expended more than half of its prewar inventory on four of the seven systems. Replacement timelines across the portfolio range from one to four years, conditional on existing pipeline deliveries arriving on schedule — a caveat with significant industrial-base sensitivity.

Open-source reporting corroborates the CSIS depletion picture. US official statements cited expenditure of “more than 1,000” BGM-109 Tomahawk Land Attack Missiles (TLAMs) and “1,500 to 2,000” AMD interceptors during the 39-day campaign. At pre-campaign production rates, replacing 1,000 TLAMs alone would require approximately five to seven years of uninterrupted Raytheon output. The AMD figure, dominated by Patriot Advanced Capability-3 Missile Segment Enhancement (PAC-3 MSE) rounds, represents several years of Lockheed Martin’s Camden, Arkansas production capacity.

Weapon System Technical Assessments

BGM-109 Tomahawk Land Attack Missile (TLAM) — Block IV / Block V

The BGM-109G/H Tomahawk is a subsonic, sea- and ground-launched cruise missile designed for long-range precision strike against fixed and relocatable targets. Block IV (Tactical Tomahawk) introduced a two-way data link enabling in-flight retargeting; Block V added the Maritime Strike Tomahawk (MST) anti-ship variant and enhanced penetrating warhead.

Precision Strike Missile (PrSM) — Block I

PrSM is the US Army’s replacement for the MGM-140 Army Tactical Missile System (ATACMS). Unlike ATACMS, which dispensed Dual-Purpose Improved Conventional Munitions (DPICM) or carried a unitary warhead, PrSM Block I carries a unitary warhead and is sized to two rounds per M142 High Mobility Artillery Rocket System (HIMARS) pod or four per M270A2 Multiple Launch Rocket System (MLRS) launcher, significantly increasing platform magazine capacity. PrSM entered limited operational service in 2023.

Patriot Advanced Capability-3 Missile Segment Enhancement (PAC-3 MSE)

PAC-3 MSE is a hit-to-kill AMD interceptor deployed within the Patriot weapon system. Unlike earlier Patriot variants (PAC-1 and PAC-2 GEM), PAC-3 MSE does not rely on proximity-burst fragmentation. It carries a small “lethality enhancer” — a collar of focused fragmentation — but the primary kill mechanism is kinetic impact. The missile uses an active Ka-band radar seeker for terminal homing, allowing engagement of tactical ballistic missiles (TBM), cruise missiles, and advanced aircraft. MSE extends range and ceiling beyond the baseline PAC-3 configuration.

Terminal High Altitude Area Defense (THAAD) Interceptor

THAAD provides upper-tier AMD, engaging TBMs in the terminal descent phase at altitudes between 40 and 150 km. The THAAD interceptor is a pure hit-to-kill system carrying no explosive payload whatsoever; the kill vehicle destroys the target through hypervelocity kinetic impact at closing speeds typically exceeding 2 km/s. THAAD is cued by the AN/TPY-2 X-band radar, which can operate in forward-based mode to extend radar horizon. The low annual production rate of THAAD interceptors makes it the most strategically sensitive of the four depleted systems.

Industrial Base Analysis: The Solid Rocket Motor Choke Point

All four of the most-depleted munitions — TLAM (booster), PrSM, PAC-3 MSE, and THAAD — share dependence on solid rocket motors (SRMs) manufactured at a small number of US facilities. The SRM supply chain is the principal industrial-base constraint limiting surge production across the portfolio simultaneously. Key facilities include Aerojet Rocketdyne at Camden, Arkansas (PAC-3 MSE and THAAD motors); Northrop Grumman Propulsion Systems at Elkton, Maryland and Rocket Center, West Virginia; and Atlantic Research Corporation. Each facility operates under safety-case-governed energetic material handling constraints that restrict throughput expansion without capital-intensive facility upgrades or new construction.

The strategic implication is that accelerating production of multiple depleted systems concurrently will produce SRM competition for the same sub-tier suppliers. The Munitions Acceleration Council and Pentagon energetics offices flagged this constraint repeatedly through 2025–26, and the FY27 budget request includes investment specifically targeting SRM sub-tier expansion — but new energetics manufacturing capacity takes three to five years to qualify and certify under AOP-7 Edition 3 and equivalent national doctrine.

Expenditure Rate vs Production Rate: Quantitative Assessment

The table below compares estimated open-source production rates against the campaign’s implied minimum expenditure, illustrating the rebuild timeline challenge. All figures are open-source estimates; classified actuals may differ materially.

Personnel, Safety and EOD Implications

For ammunition technicians (ATs), armament technicians, and EOD operators, the post-campaign inventory reset generates several immediate and medium-term considerations.

Lot-rotation compression. The inventory drawdown compresses lot-rotation cycles. Surge-rate production will introduce a higher proportion of recently manufactured lots with shorter accumulated surveillance histories. ATs should anticipate more frequent acceptance inspections, tighter lot-traceability requirements, and a greater proportion of energetic fills without a long-duration performance baseline. Compliance with DSA 03.OME (formerly JSP 482, now withdrawn) and equivalent national doctrine is mandatory throughout the surge cycle.

Unexploded ordnance (UXO) and dud rounds. At documented campaign expenditure scales, a percentage of rounds will have failed to function as designed. EOD planners and battlefield clearance units operating in or near the Iran campaign area should anticipate dud TLAMs (subsonic, turbofan-sustained; fuze state uncertain on impact), dud PrSM rounds (SRM-driven; potentially armed warhead in failed detonation state), and expended THAAD and PAC-3 MSE kill vehicles (minimal energetic risk; primary hazard is physical damage and propellant residue). The HD and Compatibility Group (CG) re-baselining requirements for new-lot surge production should be completed before those rounds enter forward stockpiles.

Hazard classification during surge transport. TLAM WDU-36/B warhead sections are HD 1.1 CG D. During surge production and acceptance movements, ATs should expect increased tempo of Class 1.1 consignments on supply routes and in ammunition storage facilities (ASFs). Quantity–distance (QD) constraints under STANAG 4439, AOP-7 Edition 3 and relevant national legislation (ADR/RID by road/rail; IMDG Code by sea) must be applied without reduction for operational tempo pressure.

Fuze states in unexpended recovered rounds. Any TLAMs recovered intact (e.g., from failed launch or emergency safing after sortie cancellation) require formal EOD assessment of fuze state before handling. The WDU-36/B warhead uses an FMU-148/B fuze; armed-state confirmation requires specialist AT or EOD assessment. Under no circumstances should recovered intact cruise missiles be handled by non-specialist personnel.

Regulatory and Standards Implications

The surge production and accelerated acceptance of seven munition types simultaneously will generate an elevated tempo of regulatory engagement between prime contractors and national safety authorities. Key regulatory touchpoints include STANAG 4439 (Policy for Introduction and Assessment of New Munitions), which requires safety assessment for any variant change introduced during surge; AOP-7 Edition 3 (NATO Guidelines for the Safety and Suitability for Service Assessment of Munitions), applicable to allied nations receiving US-manufactured rounds; and DSA 02.OME, which governs UK munitions safety case obligations for US-origin munitions entering British stockpiles under materiel-sharing arrangements. The Holston Army Ammunition Plant single-source dependency for RDX and HMX — identified as a critical vulnerability in post-campaign analyses of earlier expenditure rates — remains unresolved and applies to multiple warhead fills across the seven CSIS-assessed systems.

WOME Technical Data Gaps

• System enumeration: CSIS names seven munitions in the study but the public summary does not list all seven by designation. ISC assesses the four most-depleted likely include BGM-109 TLAM, PAC-3 MSE, and THAAD; the fourth is unconfirmed (PrSM, AIM-120 AMRAAM, or GBU-72/B assessed as candidates).
• AMD breakdown: The 1,500–2,000 AMD interceptors figure is not disaggregated between PAC-3 MSE and THAAD in open release. The ratio is operationally significant: THAAD is the more constrained production item by an order of magnitude.
• Per-system Pk: Campaign-actual Pk values for PAC-3 MSE and THAAD against Iranian TBM variants are not in open release. Post-campaign Pk data will materially revise inventory-level models for US and allied planners.
• Allied stockpile contributions: Whether allied PAC-3 MSE rounds (Israel, Japan, Germany, Netherlands) were drawn upon during the campaign is not addressed in open sources.
• Post-conflict UXO data: Fuze states, failure modes, and lot attributions of recovered failed rounds are not in open release.
• Surge contract specifics: The FY27 budget request quantities for accelerated multiyear procurement of each affected system are not yet public.

Authoritative and Editorial References (A&ER)

1. Center for Strategic and International Studies (CSIS), Last Rounds? Status of Key Munitions at the Iran War Ceasefire, April 2026. csis.org. Source reliability: A / Accuracy: 2 (STANAG 2022).
2. Raytheon Technologies / RTX Corporation, BGM-109 Tomahawk programme data. rtx.com.
3. Lockheed Martin, PAC-3 MSE programme datasheet. lockheedmartin.com.
4. Lockheed Martin, THAAD system overview. lockheedmartin.com.
5. Lockheed Martin, Precision Strike Missile programme. lockheedmartin.com.
6. NATO Standardization Office, AOP-7 Edition 3: NATO Guidelines for the Safety and Suitability for Service Assessment of Munitions. Brussels: NSO, 2020.
7. NATO Standardization Office, STANAG 4439 Edition 3: Policy for Introduction and Assessment of New Munitions. Brussels: NSO.
8. Defence Safety Authority (DSA), DSA 03.OME: Ordnance, Munitions and Explosives — Regulations. UK MoD. [Successor to JSP 482, now withdrawn.]
9. DVIDS asset 8189235 — THAAD Deployment, U.S. Army, January 2024. dvidshub.net. Public domain (17 U.S.C. § 105). Reused for editorial purposes with non-endorsement disclaimer.

AI-assisted WOME technical assessment based entirely on open-source material. Not a formal intelligence product. Classification: Open Source / Unclassified. Source reliability: A (CSIS) / Accuracy: 2 (Probably true — awaiting full CSIS data tables and official US production disclosures) under NATO STANAG 2022. All weapon system specifications derived from manufacturer open-source datasheets and published academic/defence analysis; classified figures are identified as DATA GAP throughout.