“Precision Strike Missiles” (PrSMs) in Iran War: The U.S. Obligation to Conduct a Legal Review of New Weapons

On March 4, 2026, United States Central Command (USCENTCOM) published the following post on its official Facebook page:  

In a historic first, long-range Precision Strike Missiles (PrSMs) were used in combat during Operation Epic Fury, providing an unrivaled deep strike capability.

“I just could not be prouder of our men and women in uniform leveraging innovation to create dilemmas for the enemy.” – Adm. Brad Cooper, CENTCOM Commander

On March 29th, the New York Times reported that it appeared PrSM, which was “untested in combat,” may have been used in an attack that struck a sports hall and adjacent elementary school near a military facility in southern Iran, according to weapons experts and a visual analysis by the Times. Local officials cited in Iranian media said this strike and others nearby in the city of Lamerd killed at least 21 people. On March 31, 2026, USCENTCOM issued a press release stating, “Several media outlets recently reported accusations of U.S. forces striking a sports hall and residential area in the city of Lamerd, Iran, on Feb. 28. After looking into the reports, U.S. Central Command has confirmed the accusations are false.” It went on to state that the video was not PrSM but rather it was “consistent with the dimensions and silhouette of an Iranian Hoveyzeh cruise missile.” This blanket denial, without providing much supporting evidence, has been viewed by some with skepticism.

Regardless of whether PrSM was used in this particular attack, these events and the linkage to PrSM raise the question of how the Department of Defense (DoD) and the Department of the Army test and evaluate new weapons to ensure that they can be used in compliance with the law of armed conflict (LOAC). 

This author served as the Special Assistant to the Army Judge Advocate General for Law of War Matters from 2016 until 2023 and was responsible for conducting the legal review of new weapons for the Department of the Army.  This essay will explain three matters: 

(1) The Precision Strike Missile (PrSM);
(2) The standard DoD Weapons Review Process; and
(3) How the Department of the Army as the proponent of PrSM, would ordinarily evaluate this weapon to ensure that its fielding and use are in compliance with applicable international law.   

What is the Precision Strike Missile (PrSM) 

The Precision Strike Missile (PrSM) is a long-range weapon designed for the U.S. Army and developed by Lockheed Martin to replace the Army Tactical Missile System (ATACMS) that has a maximum range of 300 kilometers. PrSM is a surface-to-surface weapon system that provides enhanced capabilities to attack, neutralize, suppress and destroy targets using missile-delivered indirect fires out to a distance of at least 499 kilometers. 

PrSM is compatible with existing launchers such as the M270A2 Multiple Launch Rocket System (MLRS) and M142 High Mobility Artillery Rocket System (HIMARS). As opposed to the existing ATACMS system, each PrSM pod carries two missiles, effectively doubling the firepower of the ATACMS system that only carried one. PrSM is designed to destroy both area and point targets, including enemy troops, armored vehicles, and air defense systems. 

Reports note that the next iteration of PrSM, which is expected in 2028, will add “multi-mode seeker combining a radar and imaging infrared sensor. This will enable the missile to detect and lock on to moving ships (it’s also called the Land-Based Anti-Ship Missile or LBASM) and perhaps moving land-based vehicles too.”   Future iterations will involve “new payloads allowing the missile to release multiple bomblets and even swarms of small kamikaze drones,” as well as extending the range to “over 620 miles.” 

The U.S. Army announced: 

“The [PRSM] achieved Milestone C approval on July 2, 2025, signaling the program’s transition into the Production and Deployment phase. PrSM Increment 1, designed to neutralize, suppress, or destroy adversary anti-access and area denial capabilities at ranges greater than 400 kilometers, represents a critical advancement in the Army’s long-range precision strike capabilities. PrSM Increment 1 will replace the Army Tactical Missile System, delivering increased range and lethality to Army field artillery formations.”  

The milestone C approval is important as this is when PrSM presumably received a legal review prior to its fielding as part of the DoD weapons review process.

DoD Weapons Review Process

The United States is not a party to Additional Protocol I to the 1949 Geneva Conventions; so there is no explicit treaty obligation to conduct legal reviews of new weapons, means or method of warfare. Some commentators note that there is “an implied obligation” to conduct such review as indicated by the practice of States prior to the adoption of Additional Protocol I. The International Committee of the Red Cross, in its 2006 Guide to the Legal Review of New Weapons, Means and Methods of Warfare, also takes the view that the requirement to assess the “legality of all new weapons, means and methods of warfare … is arguably one that applies to all States, regardless of whether or not they are party to Additional Protocol I.”  However, the DoD’s position is that there is no customary international law obligation to conduct a weapons review as “there is insufficient state practice and opinion juris.” 

The DoD Law of War Manual reiterates that long-standing U.S. policy requires a legal review of the intended acquisition of a weapon system to ensure its development and use is consistent with LOAC. This policy predates adoption of Additional Protocol I. Each military service has issued regulations implementing this policy. For example, Army Regulation 27-53 (AR 27-53) sets forth the requirements for legal reviews of new weapons and states that the legal review of the acquisition or procurement of a weapon system should occur at an early stage of the acquisition process, including the research and development phases, to ensure its legality under LOAC, domestic law, and other international law (called “Milestone B”). Even though it is important for the evaluation to be done at the earliest stages of the development or acquisition process, AR 27-53 states that “a final legal review must be made prior to the award of the initial contract for production (generally Milestone C or the equivalent) … to determine whether the [weapon] and/or its intended use is consistent with all applicable U.S. domestic law and international legal obligations of the United States, and LOAC.”   

Accordingly, a legal review of a new weapon is a critical component of ensuring that such weapons are used in compliance with international legal obligations. This process – which has been in place since 1974 and has worked very well up until now – enables service members to have confidence that the weapons they are using have undergone a rigorous process and are the best weapons possible that comply with LOAC. 

What is Considered in a Legal Review of Weapons and Weapons Systems

Once a new weapon is ready for a legal review, the procuring agency or command must submit a written request to the legal advisor designated to conduct the review.  Any request will include, at a minimum, the following information: 

1. A general description of the weapon;
2. The intended use of the weapon;
3. The reasonably anticipated effects of the weapon.  All tests, computer modeling, laboratory studies, and other technical analysis and results that contribute to the assessment of the reasonably anticipated effects should be included for review.

This information will provide the reviewer with the necessary information to conduct the legal review.  The reviewer may always request any additional information pertaining to the weapon needed to properly review the new weapon.  Once all the information necessary for the legal review of a new weapon has been provided, the reviewer will then conduct the review.  The legal review will consider the following three questions with respect to the new weapon:  

1. Whether the weapon falls within a class of weapons that has been specifically prohibited; 
2. Whether the weapon’s intended use is calculated to cause superfluous injury or unnecessary suffering; and 
3. Whether the weapon is inherently indiscriminate.

If the weapon is not specifically prohibited, the review should consider whether there are legal or policy restrictions on the intended use that are specific to that type of weapon. Finally, Section 6.2.2 of the DoD Law of War Manual provides that “it may be appropriate to advise whether other measures should be taken that would assist in ensuring compliance with law of war obligations related to the type of weapon being acquired or procured. For example, it may be appropriate to advise on the need for training programs and other practical measures, such as promulgating doctrine and rules of engagement related to that type of weapon.” 

Application of the Elements of a Legal Review to PrSM  

Under AR 27-53, PrSM was required to have undergone a legal review prior to its fielding and use in the conflict with Iran. 

Did that happen in this case?  It is unknown as weapons reviews are not made public for a variety of legitimate reasons since they often contain proprietary information as well as technical specifications that need to be protected. Accordingly, those outside the Department of Defense are not privy to the legal reviews.  Although conducting a legal review is required, this author knows from experience there have been instances where a new weapon is fielded without receiving a legal review. Past practice has always been to conduct a legal review once the reviewer is made aware that a new weapon has been fielded without a proper review.  However, there is nothing presented that would indicate that PrSM would be considered an unlawful weapon when assessed against the three questions with respect to new weapons.

Does PrSM fall within a class of weapons that has been specifically prohibited?

The first question to consider is whether PrSM falls within a specific rule of law or treaty obligation that would prohibit or restrict its use.  As Section 6.4.2 of the DoD Law of War Manual provides, those weapons would include poison, poisoned weapons, poisonous gases, and other chemical weapons; biological weapons; certain environmental modification techniques; weapons that injure by fragments that are non-detectable by X-rays; certain types of mines, booby-traps, and other devices; and blinding lasers.  Though a weapon may not be prohibited under LOAC, there may be weapons that either have LOAC restrictions or U.S. policy restricts their use.  Section 6.5.1 of the DoD Law of War Manual include in this category weapons such as mines, booby-traps, and other devices (except certain specific classes of prohibited mines, booby-traps, and other devices); cluster munitions; incendiary weapons; laser weapons (except blinding lasers); and riot control agents. 

PrSM does not fall into any of these prohibitions or restrictions. It contains a “unitary blast‑fragmentation warhead optimized for area and point targets;” it does not have submunitions so it would not be considered a cluster munition and subject to the 2017 DoD Cluster Munition Policy.    

Is PrSM’s intended use calculated to cause unnecessary suffering or superfluous injury?

The second question looks to determine whether PrSM’s use is calculated to cause unnecessary suffering or superfluous injury. The terms “unnecessary suffering” and “superfluous injury” are generally synonymous. Superfluous injury or unnecessary suffering acknowledges that the use of weapons in war causes suffering, including injury and loss of life. A weapon causes superfluous injury only when, in the normal use, it has a particular effect—and the injury caused is considered by governments as manifestly disproportionate to the military necessity for it. This determination cannot be made in isolation from other weapons. A weapon’s effects must be weighed in light of comparable, lawful weapons in use on the modern battlefield.

To determine whether a weapon causes superfluous injury, a legal review must include an evaluation of the military necessity of the weapon; an analysis of the intended results of its use (including design, that is, what it is designed to do, and intended employment, that is, how it is intended to be used in combat); and a comparison of the weapon with lawful comparable weapons already in use.

PrSM is “designed to detonate just above its target and blast small tungsten pellets outward” and its intended use is “against hardened or soft strategic targets, including enemy air defense systems, command facilities, logistics hubs, and missile launchers.” The United States has similar weapons in its inventory that perform the same function. However, it would be important for the reviewer to analyze any wound ballistic information to verify that the wounds are similar to existing weapons in the U.S. inventory.

The military necessity for PrSM is its ability to engage targets at a range far exceeding the ATACMS maximum range of 300 kilometers. This extended range allows the Army a much-needed deep fight capability.   

Is PrSM inherently indiscriminate?

Distinction is a fundamental rule of LOAC. It requires that military forces direct their attacks against enemy military objectives and distinguish these military objectives from the civilian population and civilian objects. Combatants, civilians taking a direct part in hostilities, and other military objectives may be targeted. Distinction requires that the weapon be capable of being directed against a military objective.  Indiscriminate attacks are prohibited.

In determining distinction, “capable of being directed” does not require “terminal guidance” to the final point of impacting the target or use of the most precise weapon under all circumstances.  It does prohibit “blind weapons,” which are those weapons that cannot, with any reasonable assurance, be directed against a military objective.  Indiscriminate weapons also include those that are essentially random in their effects and would be generally as likely to hit civilians as combatants.  

PrSM is a precision guided munition that is designed for high accuracy, with early reports and testing indicating a Circular Error Probable (CEP) of less than one meter, enabling it to strike precise coordinates at long ranges.  PrSM, at least as designed, is not an inherently indiscriminate weapon. As discussed above, there may be instances where other measures should be taken that would assist in ensuring compliance with law of war obligations. The New York Times states that  photos of the aftermath of the detonation of PrSM “show both sites were pockmarked with holes, apparently from the tungsten pellets. related to the type of weapon.”  Based on the information available, the blast radius of tungsten pellets is unclear. This is certainly something the legal review would address as it could affect the appropriateness of using PrSM in populated areas.  If the radius is large, the reviewer may recommend it not be used in those circumstances as that may raise issues with respect to incidental harm to civilians and civilian objects in proximity to military objectives.  

In considering the three questions that must be addressed in a weapons review, and based on the publicly available information I have been able to read, there is no reason to believe that PrSM would fail the requirements of the legal review for a new weapon and to be fielded by the United States. If the testing data confirms the information available, such as a CEP of one meter, PrSM is a lawful weapon.

The Use of PrSM in the Strike Against Iran 

The questions regarding PrSM revolve around the attack on the military facility in Lamerd in southern Iran that also reportedly struck a sports hall and adjacent elementary school and killed at least 21 people.  As the New York Times noted, “Since the weapon is so new, it’s more difficult to assess whether the PrSM strikes in Lamerd were intentional, stemmed from a design flaw or manufacturing defect, or were the result of improper target selection.”

A recent article by Annie Shiel and Priyanka Motaparthy (here) wrote that USCENTCOM is conducting an investigation into this incident to determine the reason why the strike hit the sports hall and school.  It is too early to tell what caused PrSM to strike civilian objects.  

Under LOAC, lawful weapons—those not prohibited by international law—can be used in an unlawful manner if their use violates LOAC principles of distinction and proportionality. Accordingly, if PrSM was directed at the elementary school and sports hall and they were civilian objects (i.e., not being used as a military objective by the Iranian military forces), then it would violate the principle of distinction. An attack using PrSM would violate the principle of proportionality when the expected loss of civilian life, injury to civilians, and damage to civilian objects incidental to the attack would be excessive in relation to the concrete and direct military advantage expected to be gained. 

Finally, if it is determined that the strike occurred because of a design flaw or defect with PrSM, then it should be removed from operational use until the flaws or defects are addressed and new testing and evaluation is conducted to ensure PrSM is able to be used in a manner that complies with LOAC. That is why there is both testing and the legal review process in place.  These long-standing procedures help ensure that any flaw or defect is addressed prior to fielding. 

Conclusion

The use of new weapons on the battlefield often raises concern about whether the new weapon can be used in compliance with LOAC. This is especially true with respect to PrSM in that its initial use reportedly resulted in the death of civilians and destruction of civilian objects. As my former colleague, and the individual who instituted the DoD weapons review, W. Hays Parks, noted, there are three  important reasons to ensure new weapons undergo a legal review. First, the United States is a party to law of war treaties prohibiting the use of certain weapons or munitions.  The  United States has accordingly agreed to certain obligations which it must implement in good faith. “As a nation that believes in the rule of law, it is incumbent upon the United States to ensure compliance with treaty obligations,” Hays wrote. Second, the legal review provides the program manager as well as the military commander with an approval of the legality of the weapon or munition in question. It assures commanders and service members that the weapons DoD issues to them are lawful.  Finally, a proper weapons review provides an immediate response to questions that may arise with respect to the legality of the weapon if something goes wrong on the battlefield. 

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