Specifically (in British usage) Military Aid to the Civil Power (MACP) means armed assistance to the police when the latter are unable to cope with riot, organized crime, or terrorism. More generally, the term can be used to embrace Military Aid to Civil Authorities (MACA) which also includes Military Aid to Civil Ministries (MACM), or (from July 1998) Military Aid to (other) Government Departments (MAGD) —strike-breaking—and Military Aid to the Civil Community (MACC) which is unarmed assistance in the event of natural or humanitarian disaster.
Military forces have long been used as an aid to enforcing civil law and order. In medieval and early modern times the distinction between keeping the peace at home and armed forces' international roles was blurred. Landowners retained their own armed retinues, which might be used for law enforcement or in civil or foreign wars. In Britain the posse comitatus, the armed power of the county commanded by its sheriff, could be used to meet invasion or disorder, and the concept of the ‘posse’ crossed the Atlantic to emerge in hot pursuit of malefactors in the Wild West. A doctrine of that name still governs MACP by the regular armed forces in the USA.
Following the creation of modern standing armed forces in the 17th century, but before the advent of modern police forces in the 19th, law enforcement remained a primary role of armies, whether regular or militia. The Peterloo massacre of 1819 is an infamous example of MACP going wrong. Navies were also extensively employed against smugglers and pirates—a role that differed little, except in scale, from their use against other navies. Armed forces were often unhappy with the task. Servicemen could find themselves culpable in military law for failing to act decisively, but at risk from the criminal law—perhaps represented by a hostile jury—if they were judged to have overreacted. Effective action in support of the civil power often required a level of discipline which was not easy to attain. There were fears—sometimes all too justified—that conscript soldiers would side with the rioters rather than the army, one reason for the French right's traditional mistrust of short-service conscripts.
The concept of MACA, embracing MACP, MAGD, and MACC, is peculiar to Britain and the Commonwealth because most other countries have a paramilitary ‘third force’ or gendarmerie to cover these eventualities. In France the Compagnies Républicains de Securité (CRS) are specially designed to deal with riots and those circumstances which fall awkwardly between the maintenance of law and order and war. In the former USSR and other East European countries the interior ministry had its own armed troops to deal with major riots and low-level insurrection. Armed forces proper may be constitutionally prevented from taking an internal security role. Thus, when the province of Chechnya attempted to break away from Russia in 1994 after its 1991 declaration of independence, it was the interior ministry's responsibility, not that of the armed forces. The Soviet interior ministry had entire mechanized divisions with APCs, tanks, and artillery who were better trained than the armed forces for this type of work. However, these were not sufficient and the armed forces were brought in—as ‘aid to the civil power’. In the USA, the National Guard performs a similar role, which assumed an unfortunate prominence during the protests against the Vietnam war in the 1960s: the shooting of student protesters at Kent State University was the Peterloo of its day. The US Coastguard is responsible for maritime policing tasks for which the UK would have to call on the navy.
The distinction between MACP—involving armed troops to quell riot or terrorism—and MAGD—using troops to guarantee essential services during industrial unrest and strikes—is not always clear cut. In 1911 a group of armed East European terrorists was cornered in a house in Sidney Street, east London, and killed three of the policemen who had tried to arrest them. Churchill, the Home Secretary, ordered in a detachment of Scots Guards. The besieged house caught fire and two terrorists were later found dead. This was a classic use of MACP. Later the same year there was a dock strike in Liverpool. A serious riot occurred outside Lime Street station. The local magistrate read the riot act and 2nd Battalion the Royal Warwickshire Regiment was turned out to clear the area. On 15 August a crowd tried to rescue five police vans' worth of convicted rioters being taken to the city's Walton prison. Its cavalry escort opened fire. The following days saw several bayonet charges and on 17 August the navy cruiser HMS Antrim was ordered into the river Mersey, followed by a second cruiser soon after. Again, although the root cause was a strike, armed intervention by the military was MACP, not MAGD. Churchill was quite clear about the distinction: ‘It is only when a trade dispute is accompanied by riot, intimidation or other violations of law or when a serious interruption is caused … to the supply of necessary commodities that the military can be called upon to support the police, and then their duty is to maintain the law, not to interfere in the matter of the dispute.’
The 1920 UK Emergency Powers Act clarified the confused legal position regarding the use of troops in industrial disputes. During the 1926 General Strike the military were kept in the background as far as possible. They were mainly used to protect food convoys and to guard power stations and other key points. The General Strike was the last occasion in Britain that troops intervened in a strike to keep the peace. The separation of military assistance to the civil power to deal with civil disorder (MACP) from assistance to other government departments to maintain essential services (MACM, MAGD) dates from this period. The British army's role in Northern Ireland since 1969 is the classic example of MACP. The army is there to assist the Royal Ulster Constabulary and is ultimately in a subordinate position to it. In practice, members of the armed forces, the police, and the other security services work closely together.
MACC procedures are fairly similar round the world. In the event of flood, earthquake, avalanche, or volcanic eruption the military usually respond as well as they can: they may be requested, or may volunteer their services. In the more complex security environment of the 21st century the role of military forces in these areas is likely to be enhanced, as part of a formula which has been called D3: Defence, Disaster, Development.
— Christopher Bellamy
