Armed policing

Attenuating energy projectiles

The attenuating energy projectile (AEP) forms part of the common weapon system approved for use by members of the police service or Her Majesty’s forces in the UK. Operational use of the AEP in the UK police service is limited to authorised officers who have been specifically trained in use of the system.

This guidance relates to the approved 37 mm soft nosed impact projectile, designated the L60A2. This is an AEP and is intended for use as a less lethal kinetic energy device.


The approved AEP (designated as L60A2) is fired from a 37 mm breech loaded weapon. The approved launcher is the Heckler and Koch L104A2, equipped with an approved L18A2 optical sight.

The projectile has been designed with a nose cap that encloses a void. This design feature is intended to attenuate the delivery of the impact energy by extending the duration of the impact and minimising the peak forces. It thereby delivers a high amount of energy to maximise its effectiveness, while reducing the potential for life-threatening injury.

Reducing the rate of onset of the impact force and reducing the magnitude of the peak force, have both been shown to reduce the severity of injuries in human impact.


AEP is intended to provide officers, including those issued with conventional firearms, with a differentiated use of force and firearms.

AEP will, where appropriate, be deployed alongside conventional firearms and other less lethal technologies already on issue to firearms officers.

For detailed guidance in respect of the legal framework within which lethal and less-lethal force may be used see legal framework and use of force, firearms and less lethal weapons.


The AEP is used to dissuade or prevent a potentially violent person from their intended course of action, thereby neutralising the threat. AEP use will be informed by reference to the National Decision Model (NDM), which gives officers (including those armed with conventional firearms) an additional means of dealing with threats of serious violence.

It is recognised that the use of a kinetic energy projectile has the potential for lethal consequences in certain circumstances.

Detailed instruction on the characteristics, operation and use of AEP is covered in the training and documentation provided to officers who are accredited to use it.

An ACPO AEP Discharge Form needs to be completed for every operation where the AEP is discharged.


In circumstances were firearms resources have been deployed to a situation, the authorisation for officers to use their firearm will also include the authority to use any other less lethal option or technology with which they have been issued (including, where appropriate, the AEP).

In these situations it would be inappropriate for commanders or supervisory officers to attempt to restrict officers to a particular, less lethal technology or use of force option.

The availability or deployment of the AEP should not be considered as a replacement for conventional firearms in situations where the deployment of conventional firearms has been authorised.

Public order policing

AEP exists as one of the approved less lethal options available in the UK. In certain circumstances, it may be necessary and proportionate to deploy officers who are only equipped with AEP, and not with conventional firearms, to situations of serious public disorder.

AEP is intended for use as an accurate and discriminating projectile, designed to be fired at individual aggressors, whether such aggressors are acting on their own or as part of a group. It is not designed for use as a crowd control tool.

The use of a kinetic energy device in a situation of public disorder may have a profound impact on crowd dynamics, with implications for public safety and order.  Indeed in this situation, first aid officers and medical staff may be prevented from immediately reaching potential subjects by a hostile crowd. This risk should be considered during strategic and tactical decision making.

If officers armed with the AEP system only (ie, without conventional firearms) are deployed, this requires specific authority, is outside the scope of conventional firearms operations and should be commanded by appropriately trained and accredited public order commanders.


In situations of serious public disorder an officer of at least Assistant Chief Constable (ACC) or Commander rank should authorise the availability of officers armed with AEP for operational purposes.

Once the authority to make AEP available has been granted, the authority to use AEP lies with the silver (tactical) commander. The silver commander should keep the authority to use AEPs under constant review and liaise with bronze (operational) commanders and personnel using the AEP operationally. Decision making on deployment will be based on use of the national decision model.

Officers armed with the AEP who are to be deployed within a public order situation should be fully trained to undertake the role within that context as prescribed within the National Police Firearms Training Curriculum and the National Police Public Order Training Curriculum.

Criteria for use
  • officers trained in the use of AEP may be deployed in situations of serious public disorder where its use is judged to be necessary to reduce a serious risk of:
    • loss of life or serious injury, or
    • substantial and serious damage to property where there is, or is judged to be, a sufficiently serious risk of loss of life or serious injury to justify its use
  • in assessing the risk of loss of life or serious injury occurring in a public order situation, the risks to police officers, members of the emergency services, members of the public and others should be taken into account
  • chief officer to submit a written report to the Home Secretary as soon as is practicable.

Northern Ireland

Should it be necessary to deploy officers armed with an AEP in a public order or any other situation in Northern Ireland, the Police Service of Northern Ireland (PSNI) operational instruction will be in accordance with this guidance and include additional requirements as deemed appropriate by the chief constable of PSNI to meet local legislation and oversight arrangements.


The AEP is designed to deliver an impact that is not intended to cause serious or life-threatening injury, but it of sufficient force to dissuade or prevent a violent or potentially violent person from their intended course of action thereby neutralising the threat.

However, as with all applications of force, there is a potential for unintended serious and even fatal injury either as a direct result of an impact or as a result of secondary injuries such as those caused by the subject falling.

The reaction of a person struck by the AEP will vary depending on the area of the body struck and the degree of motivation being exhibited by the individual. Persons who are under the influence of alcohol or drugs, or who are experiencing mental ill health or acute behavioural disturbance may also exhibit a  wider range of responses.

Officers using the AEP should not rely on an immediate incapacitant effect. Unless follow-up action is taken, a subject struck with an AEP may continue with their previous behaviour. Officers should, therefore, continually assess the threat being posed and consider other tactical options as necessary.

Issue and possession

The AEP will be issued only to authorised officers who have successfully completed approved ACPO training in the use of the device. The authority for the issue of AEP will, therefore, be in line with local operating procedures pertaining to the issue of such equipment in each force area.

The authorised launch platform (L104A2) may also be used for launching other projectiles, and this brings it within the scope of section 5 of the Firearms Act 1968. On duty police officers are exempt from the requirements of the legislation and do not need any additional legal authority to possess the AEP.

Officers should carry out function checks on the weapon approved to launch the AEP whenever the weapon is issued and, where, possible, prior to actual deployments.

Risk factors

The Defence Scientific Advisory Council (DSAC) sub-committee on the Medical Implications of Less-Lethal Weapons (SACMILL) has provided an independent view for the UK Government on the medical implications of using the AEP L60A2 system.

Specific advice on risk factors associated with strikes to certain parts of the body is provided in a 2005 DOMILL document. This is predicated on the system being used in accordance with guidance and zeroing instructions.

Users should be made aware that AEPs can ricochet in some circumstances. Consideration should also be given to minimising the possibility of striking individuals behind the indentified subject. The presence of obstacles and of personnel other than the intended target, and the possibility of direct strikes and strikes as a result of ricochet, should form part of the risk assessment in the decision to fire the weapon.

Mental ill health

Sometimes it may be necessary to use the AEP on a person who is exhibiting violent behaviour who is experiencing a mental disorder or illness. Where it is possible to discuss options with mental health professionals present at the scene, this should be considered.

Consultation with appropriate healthcare professionals (mental health/GRP/other), social workers, carers, friends and relatives of the subject may contribute to the implementation plan for pre-planned operations or joint activity. Relevant and appropriate information or intelligence taken from this process should form part of the briefing and may assist in deciding on the most appropriate use of force response.

The final decision on the most appropriate use of force options in these circumstances rests with the officer concerned.

Oral and visual warning

Where circumstances permit, officers should give a clear warning of their intent to use the AEP. They should give sufficient time for the warning to be heeded, unless to do so would unduly place any person at risk, or would be clearly inappropriate or pointless in the circumstances of the incident.

All officers should receive training in communicating with subjects. On first verbal contact, officers should normally:

  • identify themselves as officers and state that they are armed with an AEP
  • clarify who it is they are seeking to communicate with
  • communicate in a clear and appropriate manner.
Visual deterrents

Where weapons are fitted with torches or laser sights, officers should consider the effects of their use during any confrontation. The deliberate pointing of a weapon at an individual constitutes a use of force and may, in certain circumstances, constitute an assault.

It may, in certain circumstances, be appropriate to provide a display of officers visibly armed with an AEP launcher as this may have a deterrent effect.

Important: A visual display will, by definition, constitute a use of force and should be recorded as such.

Public order warning messages

In a public order situation, warning can be invaluable in alerting the crowd of police intentions and providing the opportunity for the crowd to disperse or remove themselves from danger.

Unless circumstances do not permit, AEPs are only to be fired after an oral warning has been given, for example, using a loud hailer or PA system to tell the crowd to disperse and informing individuals that force will be used against them.

The warning should make it clear that if individuals do not stop their violent action, force will be used without further warning. A record needs to be kept of the words used in giving the warning.

The oral warning should be given as many times as is reasonably practicable in the circumstances, ensuing that the police intention to deploy tactical options and/or use force is clearly communicated prior to use. If a tactic is to be used over a period of time, or a large area, it may be desirable to repeat the warning messages.

When the use of a specific tactical force option is imminent, a final warning should be given.

Point of aim

The AEP should be aimed to strike directly (ie, without bouncing) the lower part of the subject’s body (ie, below the rib cage). Officers are trained to use the belt-buckle area as the point of aim, at all ranges, thus mitigating upper body hits.

Unless there is a serious and immediate risk to life which cannot otherwise be countered, it is prohibited to use the AEP at less than one metre, or to aim the weapon to strike a higher part of the body at any range. In these circumstances the risk of serious and fatal injuries is increased and the firer must be able to justify the increased use of force.


Steps should be taken to ensure that early medical attention is available and provided for persons stuck by AEP. This might involve having officers ready who are trained in appropriate first aid and/or placing an ambulance on standby.

Close monitoring

Close monitoring of a subject throughout the period following a direct strike from any kinetic energy device is of utmost importance. If there are any signs of adverse or unusual reactions, medical attention should be provided immediately and, if necessary, this must be given precedence over conveying a subject to the police station.

Where officers are informed, or believe, that someone has been struck by the AEP has a pre-existing medical condition that might lead to increased medical risk, immediate transfer to hospital should be considered.

Medical assessment

A forensic medical examiner must examine all arrested persons who have been struck by an AEP as soon as practicable.


Information that a person has been struck by an AEP should be passed immediately to the custody officer when booking-in.

The appropriate level of observation and monitoring of the detainee will be decided through risk assessment. The minimum level of supervision that is appropriate for a detainee who has been struck by an AEP is Level 2 Intermittent Observation.

Persons at increased risk

Experience from previous incidents involving the use of any form of force has shown that some people will be at increased risk from potential harm, particularly those who are under the influence of alcohol and/or drugs or individuals who have any existing medical condition/illness.

If a person is exhibiting violent behaviour, it may be caused by an underlying medical problem or illness (see acute behavioural disturbance). Where this is suspected, the individual should be treated as a medical emergency and conveyed directly to hospital.

In the event of a child or physically vulnerable person being struck with an AEP, they should receive immediate medical assessment and be conveyed directly to hospital.


Appropriate post-incident procedures need to be implemented following the operational firing of the AEP. The appropriate procedure will depend on the nature of the injury or harm caused or will be in accordance with the specific instruction pertaining in the force area where the firing took place.

The welfare of principal officers must be considered when undertaking any investigation following a critical incident, even where little or no injury has been caused.

Evidential collection of equipment

Evidential recovery of fired AEP and spent cartridge cases should be undertaken in accordance with the APP guidance on secure firearms and ammunition.


All firings of an AEP must be immediately reported, initially by radio, and later using the ACPO AEP Discharge form. The report includes a requirement to detail:

  • the reason for firing the AEP
  • information about the outcome
  • the number of rounds fired
  • any known injuries that may have occurred as a result of using AEPs.

An investigation will be undertaken in accordance with the criteria for a post-incident investigation.

An ACPO AEP Discharge form must also be completed for every operation where the AEP is discharged.

If used in a situation of public disorder in England and Wales, the chief officer should supply the home secretary with a written report on the circumstances surrounding the firing of AEPs as soon as possible after the incident. Similar arrangements exist in Scotland. In Northern Ireland there is a requirement to inform the Northern Ireland Policing Board and the Police Ombudsman of any operational discharge of an AEP.


Operational use will be subject to monitoring and review at regular intervals to ensure that any emerging issues are properly reflected in training and operational guidance.

Representatives of the Scientific Advisory Council on the Medical Implications of Less-Lethal Weapons (SACMILL) will be invited to contribute to the process.

The ACPO AEP Discharge form must be completed on every occasion that an AEP is discharged during a policing operation where the use of firearms has been authorised.

Operational guidance and policy on the use of AEP is subject to regular review.

Unintentional discharge

Any unintentional discharge in a non-operational situation where there has been no danger to the public will be subject to an internal investigation.

In such cases referral to an IIA will be a matter for individual force management, in accordance with local policy directives.


Proper maintenance of the AEP launch platform and sights is vitally important.

It is essential that weapon function checks are carried out when the weapon is issued and that these are repeated whenever possible, prior to deployment or intended use.

Any weapon or munitions failures should, in addition to any local force instructions, be reported to the Home Office Centre for Applied Science and Technology (CAST). In the event of a misfire, appropriate post incident procedures should be implemented which conform to the ACPO AEP Discharge Form.


Electrical devices should not be stored alongside pyrotechnics, ammunition, specialist munitions or flammable products. Individual forces should undertake appropriate risk assessments in respect of storage and carriage – see the AEP Generic Risk Assessment.

Relevant legislation and guidance on storing the attenuating energy projectile (AEP):

Zeroing instructions

Qualification and zeroing of weapons must take place using the operationally approved L60A2 AEP. The AEP’s launcher must be zeroed for the individual officer and this must be performed in accordance with the zeroing instructions set out in the ACPO documentation. It is mandatory that the sight and the gun combination is zeroed to the individual by live firing.

The firer cannot zero the weapon until they can achieve a five-round group size at the specified range (five-round group in 200 mm area at 20 metres).

Collimators are individually numbered and should be matched to the firers. Provided firers use the same collimator they can apply their readings to any weapon. Weapons must be bore sighted, zeroed and the personal zero point (PZP) recorded using the same firer/collimator combination.

Under no circumstances must a different collimator be used to check PZP. If this is necessary, the weapon must be re-zeroed and the reading re-taken.


Standards of competence, training requirements and assessment for the use of AEP are set out in the National Police Firearms Training Curriculum and the National Police Public Order training Curriculum. These standards apply to everyone who:

  • uses the system
  • provides tactical advice on its use
  • might be called on to command operations.

Throughout the UK there are:

  • AFOs trained in the use of the AEP system (as a less lethal option in any situation to which they are deployed)
  • AFOs who are additionally trained to use the AEP system within the context of serious public disorder
  • officers who are not AFOs but are specifically trained to use the AEP system (for potential use in a serious public disorder situation).

Officers must understand and appreciate the physical and psychological effects of an AEP strike.

In forces where officers authorised in the use of AEP are not trained in conventional firearms, the training provided will include an understanding of  issues associated with ricochet potential.

Page last accessed 09 April 2020