The “Shift Cold” Military Tactic and International Humanitarian Law

“Shift cold,” the practice of deliberately diverting a guided munition in flight away from its intended target, is increasingly drawing attention within the legal community.  In this contribution, we begin by explaining the practice from an operational perspective.  We do so with some granularity, for it is one with which few beyond the uniformed operational law community are familiar.  The context laid, the remainder of the piece is devoted to unpacking the legal issues that are raised by the shift cold practice.

The operational practice of “shift cold”

A “shift cold” occurs when an operator (e.g., a pilot, weapon systems operator in an aircraft, unmanned aerial system sensor operator, or someone on the ground like a member of a special forces team) redirects a guided munition, such as a missile or guided bomb, away from its initially-intended point of impact to another location while the munition is in flight (that is, post-launch or release).  This is generally done to avoid harm to civilians or to friendly forces in the target area who, at the time of weapon launch or release, were not expected to be there.

To illustrate, assume the target engagement authority has authorized an aerial strike on an enemy leader with an expectation that he will be alone in an isolated area when attacked. As the sortie is being executed, the pilot scans the target area and confirms that there are no collateral concerns, that is, that civilians are not present.  However, after the weapon is released but before impact, a video feed from an unmanned aerial system (UAS) reveals civilians entering the area.  To avoid harming them, the pilot guides the weapon into an area where he or she determines that no collateral harm is likely.  This is a shift cold.

Although the term “shift cold” is not found in official US military doctrine, it is a well-understood “tactic, technique, and procedure” (TTP) for the mitigation of possible civilian harm during air strikes.  It is one employed by the US and its partners in Afghanistan and in the fight against ISIS in Iraq and Syria.  Shift cold options are also employed, for instance, by the Israeli Air Force to avoid harming civilians.

The shift cold falls into the TTP category of “post-launch abort,” or “PLA,” which the DoD’s Dictionary of Military and Associated Terms defines as “[d]eliberate action taken post-separation to cause a precision munition to miss its target.”  Details regarding the tactical application of this TTP are generally found in either theater-specific air component Special Instructions (SPINS) or in the rules of engagement (ROE), both of which are typically classified.

Whether a shift cold is an option for a given strike depends on a number factors.  First, the munition being employed matters, both in terms of control and expected effects.  Only certain precision guided munitions (PGMs), primarily laser-guided weapons (LGW), can be redirected.  Non-laser guided munitions, such as those that are GPS and inertia-guided, are usually used for pre-planned (“deliberate”) attacks on fixed targets like buildings.  Their desired point of impact is pre-programmed prior to release, making a shift cold—an inherently post-release activity—typically not an option.

Laser guided weapons include laser guided bombs (LGBs) like the Paveway II, Paveway III, or Laser JDAM (LJDAM) GBU-54.  They can be dropped from a host of aircraft, with their explosive force dependent on the size of the bomb (typically in the 500, 1000, or 2000-pound class).  It is also possible to employ a shift cold with laser guided rockets like the Advanced Precision Kill Weapon System (APKWS), which are generally associated with the A-10 aircraft. Most attention when discussing the shift cold, however, focuses on the AGM-114 Hellfire, a laser-guided missile (LGM) fired from platforms such as the MQ-1 Predator or MQ-9 Reaper UAS.

In general, LGWs require a laser target designator to highlight the intended target, and a seeker and guidance kit for the munition that enables the weapon to track and guide to the designated target.  The designator can be mounted on the attacking aircraft itself. Alternatively, the aircraft launching the strike might rely on a “buddy-lase,” that is, a laser from another aircraft or from ground forces.

Certain considerations determine the viability of a shift cold.  In particular, the weapon’s flight time is critical.  Depending on the type of weapon (gravity-based bombs or propelled rockets and missiles), the altitude from which it is released (high altitude bombs versus low altitude rockets), and the standoff distance from which it is fired (that is, distance from the target), flight time can vary from under 30 seconds to over a minute.  The longer the flight time, the greater the opportunity for civilians to unexpectedly enter the target area; yet, the longer the flight time, the wider the window during which operators can react and effectively guide the munition to another point of impact.  Conversely, the shorter the flight time, the less likely the prospect of civilians entering the area, but the narrower the window to execute a shift cold should that happen.  This is because the TTP must allow not only for a human decision, but also the physics of meaningfully altering the point of impact.

The type of weapon also plays a part in the distance and time needed to effectively alter the point of impact.  A missile generally has greater agility and is able to land farther away in less time than a bomb, which uses gravity and a tail kit to navigate.  Compounding this factor is the size of the weapon’s effect.  For instance, because a 2000-pound Paveway III has a substantially larger blast radius than a much smaller Hellfire (often armed with an under 20-pound warhead), it would have to travel an even greater distance from the original point of impact to mitigate the risk to the unexpected civilians.

Other practical considerations can affect the feasibility of a shift cold redirect during an attack.  There must be real-time video feed, unimpeded by clouds or bandwidth challenges, with adequate fidelity to discern collateral damage concerns.  There must also be prior knowledge of the target, its anticipated military value, and any risk of collateral damage at the new point of impact—all of which have to be assessed in the weapon’s flight time, and by a person at the appropriate level of command and control to possess the requisite knowledge. For example, if the pilot concerned knows that a target in the middle of the desert has only nominal value, and a significant collateral concern appears, the decision to shift cold is relatively simple.  In other situations, such as a known high-value target and nominal collateral concern, the decision may be less clear.

If planners have adequate time and intelligence resources, they may be able to identify potential shift cold points of impact near a target area in the event that the technique becomes necessary.  However, many targeting scenarios, particularly those involving time sensitive or dynamic targeting, occur in the face of less intelligence, less understanding of how the ongoing hostilities will be affected by the attack, and less understanding of the objects and pattern of life in the vicinity of the desired and alternate points of impact than with deliberate targeting. Such challenges are also especially daunting when conducting attacks into urban or other populated areas.

It must be cautioned, as noted in Joint Publication 3-09.3, Close Air Support, that post-launch abort is “a procedure of last resort” due to the limited circumstances in which it can be safely employed.  Further, the publication states that it should be used in “rare cases” and “should not be briefed as a viable option to decision makers to reduce collateral damage” in the planning stage of operations.  This is due to the potentially unpredictable and perilous outcomes of the tactic and the extremely short window available to execute it.  Nonetheless, under the right circumstances, a shift cold may provide an opportunity to avoid the risk of unacceptable collateral damage that arises unexpectedly after the launch of a strike.

The law of armed conflict and “shift cold”

Shift cold is a paradigmatic example of an international humanitarian law-required “precaution in attack” codified in Article 57 of Additional Protocol I to the 1949 Geneva Conventions. Pursuant to Article 57(1), “in the conduct of military operations, constant care shall be taken to spare the civilian population, civilians and civilian objects.”  As noted in the ICRC’s Commentary to the Article, this provision supplements Article 48, which sets forth the principle of distinction, one of two “cardinal principles” of IHL: “the Parties to the conflict shall at all times distinguish between the civilian population and combatants and between civilian objects and military objectives and accordingly shall direct their operations only against military objectives.”  A shift cold would appear to epitomize both the constant care rule and the distinction principle, at least when executed to avoid harming civilians.

Most significant with respect to the shift cold, however, is the cancellation or suspension requirement set forth in Article 57(2)(b):

An attack shall be cancelled or suspended if it becomes apparent that the objective is not a military one or is subject to special protection or that the attack may be expected to cause incidental loss of civilian life, injury to civilians, damage to civilian objects, or a combination thereof, which would be excessive in relation to the concrete and direct military advantage anticipated.

This provision was designed to apply to those executing an attack and facing precisely the situation in which most shift cold maneuvers occur.  Of course, a shift cold may be executed to avoid fratricide or for reasons unrelated to the rule of proportionality, as when a policy-determined civilian casualty cap would be exceeded if the planned point of impact were struck, even though the total number of civilians harmed would not be excessive relative to the military advantage anticipated to accrue from the attack.  But if an attacker, specifically someone with the authority to order the shift cold or who has control of the weapon, is capable of ordering or executing a shift cold in a situation in which he or she concludes civilian harm will be excessive, and there is an identified point of impact with no or significantly less expected civilian harm, it is difficult to fashion an argument that there would not be an obligation to do so.

Most States, the ICRC, and the majority of international humanitarian law experts, including those experts who prepared the Harvard Manual on the International Law Applicable to Air and Missile Warfare, consider the provisions of Additional Protocol I, which we have discussed, to be reflective of customary international law.  The precise position of the United States on the multiple facets of the requirement to take precautions in attack set forth in Article 57 is somewhat unclear.  However, this is not the case with regard to the general requirement to take precautions or the requirement relating to cancellation and suspension.  The Department of Defense’s Law of War Manual observes that “Combatants must take feasible precautions in planning and conducting attacks to reduce the risk of harm to civilians and other persons and objects protected from being made the object of attack” (para. 5.11). And it offers “cancelling or suspending attacks based on new information raising concerns of expected civilian casualties” as an example of a feasible precaution.

In a 2016 update, the Manual offered the shift cold to illustrate the cancellation and suspension option:

Subordinates generally would not be authorized to suspend or cancel attacks contrary to specific military orders because they disagree with the commander’s decisions and judgments in relation to the principle of proportionality. However, subordinate commanders or engagement authorities would be required to report promptly new information of expected civilian casualties or to cancel or suspend attacks in appropriate circumstances. For example, aircrews have refrained from conducting an attack or have redirected a munition toward a different impact location when concerns about civilian harm have become unexpectedly apparent (italics added).

Subordinates should also generally be understood to have the authority to make decisions required by the law of war, such as the decision to cancel or suspend an attack in light of new information, in order to effectuate the commander’s intent. This is especially true when those commanders will not be able to maintain situational awareness of the risks of civilian casualties.

From a humanitarian perspective, the ability to shift cold is a positive development.  The same is true from a military perspective because the causation of civilian casualties is never, as such, beneficial to the prosecution of a military campaign.  When available, a shift cold option avoids situations in which an attack is authorized and executed in the reasonable belief that the expected collateral damage will not be excessive, but the attacker learns that the actual collateral damage will be excessive when it is too late to cancel or suspend.

Some concern seems to be surfacing about the shift cold practice.  One queries what IHL requires when there is no predesignated safe redirect location (as will frequently be the case in dynamic targeting), when civilians are unexpectedly in a predesignated safe spot, when operating in a populated area or under fluid conditions, or in situations of uncertainty?  More precisely, what does IHL require of an attacker who knows that civilians will or may be killed in the vicinity of the point of impact to which a weapon might be redirected?

Redirecting a munition into an area in which civilians are present is not a deliberate attack on a civilian target; it is a continuation of an ongoing attack rather than a separate attack. Same aircraft, same weapon, and same personnel in control of the weapon, and the act can best be described as guiding the weapon away from a point.  Besides, a contrary interpretation would make it a war crime (attacking civilians) to spare civilians in the original target area by redirecting the weapon into an area where fewer civilians are at risk of harm; in other words, the law would operate to require causing greater civilian harm than would otherwise be feasible.  Such an approach not only would be contrary to the object and purpose of IHL, it would be illogical.  Clearly, the shift cold is mitigation of the harmful effects on civilians in compliance with the requirement to cancel or suspend an attack should the end result be to knowingly cause excessive civilian harm.

A better question is whether a shift cold is permissible in circumstances in which it is executed in order to avoid unexpected friendly casualties, but it will likely cause civilian casualties in the area into which the weapon is redirected.  We suggest that there is no formulaic answer to this situation.  As noted, it is our view that the shift cold is not a new attack.  Instead, the attack has unfolded in a way that was not foreseeable when planned and executed.  Accordingly, the expectation of collateral harm to civilians during the attack if the weapon is redirected, even if now disproportionate to the original military advantage, does not per se require continuing the attack using the original point of impact and likely harming friendly forces. To be clear, by “not per se” we mean this is not necessarily required based on those facts alone. It would require a deeper analysis of additional considerations to determine whether the cold shift is unlawful.

In our view, the situation in which civilians in the redirect area are harmed in an effort to avoid friendly fire is governed by the rule of proportionality.  In much the same way that the presence of unexpected civilians in the target area can alter the proportionality equation, so too can the presence of friendly forces who are placed at risk.  Survival of the unanticipated friendly forces can be treated as the revised anticipated military advantage in the calculation, while the harm to civilians in the redirect area qualifies as a revised collateral damage expectation.

The appropriateness of considering the potential harm to friendly forces is demonstrated analogously in the applicability of the proportionality rule to operations designed to defend one’s own forces, as well as consideration of risk to the attacking forces when determining whether precautions in attack are feasible.  States treat feasibility as including military considerations, a point acknowledged by the ICRC.  Thus, it is fair to take into account the harm that will be caused to friendly forces if the original point of impact is maintained.

It must be emphasized in this regard that proportionality calculations in such cases are not subject to a simple numerical comparison such that, for instance, the attacking State must suffer the harm to its forces if the number of civilians harmed by the redirect is larger.  The military advantage of avoiding harm to one’s own forces has always been seen as especially high, for both tactical and operational reasons.  Ultimately, the matter comes down to making a “reasonable” call in light of the degree of harm to the friendly forces and the civilians; commanders and others in authority must act as would reasonable persons in the same or similar circumstances.

We understand that this conclusion may appear unsatisfactory to those far from the battlefield who seek definitive legal or moral answers to the life and death dilemmas posed by combat, but it reflects the reality of warfare.  Combatants are not entitled under IHL to conduct risk-free warfare at the expense of the civilians, nor are they required by that body of law to take unwarranted risk to avoid harming them.  Rather, each case must be evaluated on its own merits with sensitivity to the balance between military necessity and humanitarian considerations that underpins IHL.  Although this admittedly equivocal standard affords combatants a wide margin of appreciation, the fog of war has long been accompanied by the fog of law.

The views expressed are the authors’ own and do not necessarily represent those of the US government, the US Department of Defense, the US Navy or the US Air Force.

[Editor’s note: Interested in this topic? Read on: Adil Haque’s The “Shift Cold” Military Tactic: Finding Room Under International Law]

(Tom Reynolds/U.S. Air Force/Getty Images)


About the Author(s)

Michael Schmitt

Chair of Public International Law at the University of Exeter Law School in the United Kingdom, Charles H. Stockton Professor at the U.S. Naval War College’s Stockton Center for the Study of International Law, Francis Lieber Distinguished Scholar at the U.S. Military Academy at West Point, Director of Legal Affairs for Cyber Law International Follow him on Twitter (@Schmitt_ILaw).

Lt. Col. Matthew King

Judge Advocate in the US Air Force currently serving in the Headquarters Air Force Operations and International Law Directorate (AF/JAO).