Low-intensity conflict
Investigations also revealed significant collusion between British state forces and loyalist paramilitaries, and furthermore loyalist paramilitaries such as the Glenanne gang included serving members of the Ulster Defense Regiment and Royal Ulster Constabulary.

Guerrilla warfare: the main challenge to low-intensity warfare: Low-intensity warfare's main opponent is the guerrilla, or irregular fighter. This opponent may be state sponsored, or private non-state actors driven by religious or other ideology in urban, semi-urban and rural areas. Modern guerrilla warfare at its fullest elaboration is an integrated process, complete with sophisticated doctrine, organization, specialist skills and propaganda capabilities. Guerrillas can operate as small, scattered bands of raiders, but they can also work side by side with regular forces or combine for far-ranging mobile operations in squad, platoon or battalion sizes or even form conventional units. Based on their level of sophistication and organization, they can shift between all those modes as the situation demands, as guerrilla warfare is flexible, not static.
Guerrilla tactics are based on intelligence, ambush, deception, sabotage, and espionage, undermining an authority by long, low-intensity confrontation. It can be quite successful against an unpopular foreign or local regime, as demonstrated by the Vietnam War. A guerrilla army may increase the cost of maintaining an occupation or a colonial presence above what the foreign power may wish to bear. Against a local regime, guerrillas may make governance impossible by terror strikes and sabotage or even a combination of forces to depose their local enemies in conventional battle. Those tactics are useful in demoralizing an enemy and raising the morale of the guerrillas. In many cases, guerrilla tactics allow a small force to hold off a much larger and better equipped enemy for a long time, as in Russia's Second Chechen War and the Second Seminole War fought in the swamps of Florida, United States. Guerrilla tactics and strategy are summarized below and are discussed extensively in standard reference works such as Mao's On Guerrilla Warfare.

Three-phase Maoist model: 

Mao/Giap approach: Mao's theory of people's war divides warfare into three phases. In the first phase, the guerrillas gain the support of the population by attacking the machinery of government and distributing propaganda. In the second phase, escalating attacks are made on the government's military and vital institutions. In the third phase, conventional fighting is used to seize cities, overthrow the government, and take control of the country. Mao's seminal work On Guerrilla Warfare, has been widely distributed and applied, nowhere more successfully than in Vietnam, under the military leader and theorist Võ Nguyên Giáp. Giap's People's War, People's Army closely followed the Maoist three-stage approach but with greater emphasis on flexible shifting between mobile and guerrilla warfare, and opportunities for a spontaneous "general uprising" of the masses, in conjunction with guerrilla forces.

Organization: Guerrilla organization can range from small local rebel groups with a few dozen participants to tens of thousands of fighters, deploying from tiny cells to formations of regimental strength. In most cases, there is a leadership aiming for a clear political objective. The organization is typically structured into political and military wings, sometimes allowing the political leadership plausible deniability of military attacks. The most fully elaborated guerrilla warfare structure was seen by the Chinese and Vietnamese communists during the revolutionary wars of East and Southeast Asia.
A simplified example of this more sophisticated organizational type, which was used by revolutionary forces during the Vietnam War, is shown below.

Types of operations: Guerrilla operations typically include a variety of attacks on transportation routes, individual groups of police or military, installations and structures, economic enterprises, and targeted civilians.  Attacking in small groups and using camouflage and often captured weapons of that enemy, the guerrilla force can constantly keep pressure on its foes and diminish its numbers and still allow escape with relatively few casualties. The intention of such attacks is only military but also political in aiming to demoralize target populations or governments or by goading an overreaction that forces the population to take sides for or against the guerrillas. Examples range from chopping off limbs in various internal African rebellions to the suicide bombings of Palestine and Sri Lanka to sophisticated maneuvers by Viet Cong and NVA forces against military bases and formations.

Surprise and intelligence: For successful operations, surprise must be achieved by guerrillas. If the operation has been betrayed or compromised, it is usually called off immediately. Intelligence is also extremely important, and detailed knowledge of the target's dispositions, weaponry, and morale is gathered before any attack. Intelligence can be harvested in several ways. Collaborators and sympathizers usually provide a steady flow of useful information. If working clandestinely, guerrilla operatives may disguise their membership in the insurgent operation and use deception to ferret out needed data. Employment or enrollment as a student may be undertaken near the target zone, community organizations may be infiltrated, and even romantic relationships struck up in intelligence gathering. Public sources of information are also invaluable to the guerrilla, from the flight schedules of targeted airlines, to public announcements of visiting foreign dignitaries, to US Army Field Manuals. Modern computer access via the World Wide Web makes harvesting and collation of such data relatively easy. The use of on the spot reconnaissance is integral to operational planning. Operatives will "case" or analyze a location or potential target in depth- cataloging routes of entry and exit, building structures, the location of phones and communication lines, the presence of security personnel, and a myriad of other factors. Finally, intelligence is concerned with political factors such as the occurrence of an election or the impact of the potential operation on civilian and enemy morale.

Relationships with the civil population: Relationships with civil populations are influenced by whether the guerrillas operate among a hostile or friendly population. A friendly population is of immense importance to guerrillas, providing shelter, supplies, financing, intelligence, and recruits. The "base of the people" is thus the key lifeline of the guerrilla movement. In the early stages of the Vietnam War, American officials "discovered that several thousand supposedly government-controlled 'fortified hamlets' were in fact controlled by Viet Cong guerrillas, who 'often used them for supply and rest havens.'" Popular mass support in a confined local area or country, however, is not always strictly necessary. Guerrilla and revolutionary groups can still operate by using the protection of a friendly regime, drawing supplies, weapons, intelligence, local security, and diplomatic cover. The Al Qaeda organization is an example of the latter type, drawing sympathizers and support primarily from the wide-ranging Muslim world, even after American attacks eliminated the umbrella of a friendly Taliban regime in Afghanistan.
An apathetic or hostile population makes life difficult for guerrillas, and strenuous attempts are usually made to gain their support. They may involve not only persuasion but also a calculated policy of intimidation. Guerrilla forces may characterize a variety of operations as a liberation struggle, but that may or may not result in sufficient support from affected civilians. Other factors, including ethnic and religious hatreds, can make a simple national liberation claim untenable. Whatever the exact mix of persuasion or coercion used by guerrillas, relationships with civil populations are one of the most important factors in their success or failure.

Use of terror: Terror is used to focus international attention on the guerrilla cause, liquidate opposition leaders, extort cash from targets, intimidate the general population, create economic losses, and keep followers and potential defectors in line. The widespread use of terror by guerrillas and their opponents is a common feature of modern guerrilla conflicts, with civilians attempting to mollify both sides. At times, a civil population may be the main targets of guerrilla attacks, as in Palestinian operations against Israeli civilians. Such tactics may backfire and cause the civil population to withdraw its support or to back countervailing forces against the guerrillas.

Withdrawal: Guerrillas must plan carefully for withdrawal once an operation has been completed or if it is going badly. The withdrawal phase is sometimes regarded as the most important part of a planned action, as getting entangled in a lengthy struggle with superior forces is usually fatal to insurgent, terrorist or revolutionary operatives. Withdrawal is usually accomplished using a variety of different routes and methods and may include quickly the scouring of the area for loose weapons, the cleaning-up of evidence, and the disguising as peaceful civilians. In the case of suicide operations, withdrawal considerations by successful attackers are moot, but such activity as eliminating traces of evidence and hiding materials and supplies must still be done.

Logistics: Guerrillas typically operate with a smaller logistical footprint than to conventional formations, but their logistical activities can be elaborately organized. A primary consideration is to avoid depending on fixed bases and depots, which are comparatively easy for conventional units to locate and destroy. Mobility and speed are the keys; wherever possible, the guerrilla must live off the land or draw support from the civil population in which it is embedded. In that sense, "the people" become the guerrilla's supply base. The financing of terrorist or guerrilla activities ranges from direct individual contributions (voluntary or non-voluntary) to the actual operation of business enterprises by insurgent operatives to bank robberies and kidnappings to the complex financial networks that are based on kin, ethnic and religious affiliation used by modern jihadist/jihad organizations.
Permanent and semi-permanent bases form part of the guerrilla logistical structure, which are usually located in remote areas or in cross-border sanctuaries that are sheltered by friendly regimes.