31MAY

Arrow-3 81% gone; full depletion looming

2 min read

09:14UTC

RUSI projected Arrow-3 stocks fully exhausted by end of March, with $26 billion spent on 11,294 munitions in the first 16 days alone.

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ConflictDeveloping

Key takeaway

Israel may have entered April without its primary ballistic missile defence shield.

The Royal United Services Institute projected that Israel's Arrow-3 interceptor stocks were 81.33% depleted by 26 March and would be fully exhausted by the end of the month. ¹ In practical terms, fewer than one in five of Israel's pre-war upper-tier interceptors remained five days ago. The US THAAD system faces similar pressure, with stocks potentially exhausted within one month at current expenditure rates.

The cost figures behind the depletion expose a structural asymmetry. The US-Israel coalition fired 11,294 munitions in the first 16 days at an estimated cost of $26 billion. At that rate, the unfunded $200 billion supplemental request covers roughly four months of operations. The interception rate held at 92%, but Iran's missiles cost a fraction of the interceptors that destroy them. By RUSI's estimate, Iran spends roughly $1 for every $10 the coalition spends to counter it.

Replenishment takes years, not months. Arrow-3 production depends on complex supply chains and specialist components. Iran's deployment of a cluster warhead on the same day may reflect awareness that the defence gap is imminent. If RUSI's projection held, Israel entered April with no upper-tier missile defence. The next cluster warhead arrives into open sky.

Deep Analysis

In plain English

Israel's main defence against long-range Iranian missiles is called Arrow-3. Think of it as a very expensive interception system that shoots down incoming missiles before they land. Each interceptor missile costs several million pounds. RUSI, a respected British defence think tank, estimated that by 26 March, roughly four in five of Israel's pre-war supply had been used up. The projection was that the last ones would be fired by end of March. Replacing them takes years, not weeks. Iran's missiles cost far less to build than the interceptors that destroy them. Iran fired 1 for every £10 spent defending against it. If the shield is empty, Iranian missiles arrive undefended.

What could happen next?

Risk
If Arrow-3 stocks are genuinely exhausted, Iran's ballistic missiles arrive uncontested at Israeli cities, and THAAD becomes the sole remaining upper-tier defence with its own stocks draining.
Immediate · 0.75
Consequence
The cost-exchange ratio forces a strategic choice: continue operations at $800 million per day with no replenishment path, or negotiate before the THAAD gap similarly opens.
Short term · 0.8
Consequence
Arrow-3 depletion removes the deterrent value of the interception system; Iran's operational calculus on strike tempo changes immediately.
Immediate · 0.8

Source Landscape

This story draws on neutral-leaning sources

Primary parallel: The 1973 Yom Kippur War's most dangerous phase came when Israeli ammunition stocks approached exhaustion on Day 8. The US emergency airlift on Day 9 changed the strategic balance within 24 hours. Arrow-3 production timelines of years, not days, mean no equivalent airlift solution exists for this depletion.

Counter-parallel: NATO's ammunition depletion during the 1999 Kosovo campaign produced diplomatic pressure for a quick settlement rather than tactical collapse. The difference is Kosovo involved no direct threat to coalition cities; Israel faces ballistic missiles targeting population centres.

At $800 million per day in US spending, interceptor replenishment is the single largest line item in the unfunded supplemental. Arrow-3 missiles cost approximately $3.5 million each; THAAD interceptors cost approximately $10 million each. At the 11,294-munitions-in-16-days expenditure rate, the $200 billion supplemental covers roughly four months of operations before further funding is required.

Replenishment production cannot be accelerated to wartime pace in weeks. Elbit Systems and Boeing, the primary Arrow-3 manufacturers, operate on multi-year production contracts. The gap between exhaustion and replenishment is measured in years, not the months that a Congressional vote might eventually authorise.

Consensus view: RUSI's Justin Bronk and the International Institute for Strategic Studies both assess the cost-exchange ratio as strategically unsustainable. At $1 Iranian launch cost for every $10 in coalition interception cost, Arrow-3 exhaustion was predictable from Day 1 of high-tempo operations.

Counter-view: Israeli Defence Ministry sources cited by Haaretz suggest the 81.33% depletion figure conflates different Arrow variants and does not account for transferred US stocks. RUSI's single-source estimate may overstate the severity of the gap.

Key tension: Whether Israel entered April genuinely without upper-tier missile defence, or whether undisclosed US transfers have bridged the gap before the cluster warhead threat fully materialises.

Sources:Defence Security Asia (citing RUSI)

Mentions:THAAD →RUSI →Arrow-3 →

First Reported In

Update #53 · Trump drops Hormuz goal; toll becomes law

Defence Security Asia (citing RUSI)· 31 Mar 2026

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Causes and effects

Caused by

One ship through Hormuz in 24 hours

High missile interception rates across March drove the Arrow-3 depletion trajectory that RUSI projected would reach exhaustion by end of March.

Occurred 29 Mar 2026

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This Event

Arrow-3 81% gone; full depletion looming

If the projection held, Israel entered April without upper-tier ballistic missile defence for the first time since the system became operational.

Different Perspectives

Iran human rights monitors (Amnesty International, Iran HRM, Hengaw)

Monitors documented 30 women held on capital moharebeh charges in a basement prison ward, Benyamin Naqdi's death sentence with a forced-confession broadcast, and 39 political executions since February. Iran's security courts have processed protest cases at uninterrupted wartime tempo regardless of the diplomatic track.

Lloyd's of London (war-risk underwriters)

Lloyd's held its Hormuz war-risk designation at $10-14 million per voyage while Brent fell 19%, maintaining a structural divergence from futures pricing. Underwriters require a UN Security Council resolution or government certification letter, not diplomatic optimism, before de-listing the strait.

Oman (Sultan Haitham's government)

Muscat issued a mine alert in its own territorial waters while denying any Hormuz toll plan after US Treasury threatened sanctions. A suspected mine in Omani waters on the same weekend as US financial pressure forces Muscat to demonstrate sovereignty without appearing to choose sides.

China (PRC)

Beijing sent scholars rather than its defence minister to Shangri-La for the second year running and addressed Taiwan and multilateralism without mentioning Iran. China maintains its bilateral energy corridor protection with Tehran while refusing the diplomatic exposure of a public position at multilateral forums.

Iran Supreme National Security Council

The SNSC framed the unsigned MOU as a 10-point Iranian victory with enrichment already recognised, and the foreign ministry rejected Trump's nuclear conditions within hours. Tehran treats each unsigned day as validation that Iran has retained its stockpile without surrendering it.

Trump administration (CENTCOM/White House)

Trump posted three non-negotiable public conditions while CENTCOM disabled a commercial ship and Hegseth threatened resumed strikes from Singapore. The administration treats the unsigned MOU as leverage to extract maximum Iranian concessions before any ceasefire instrument is committed to paper.