Maritime patrol is the task of monitoring areas of water. Generally conducted by military

Military

A military is an organization authorized by its greater society to use lethal force, usually including use of weapons, in defending its country by combating actual or perceived threats. The military may have additional functions of use to its greater society, such as advancing a political agenda e.g...

 and law enforcement agencies

Law enforcement agency

In North American English, a law enforcement agency is a government agency responsible for the enforcement of the laws.Outside North America, such organizations are called police services. In North America, some of these services are called police while others have other names In North American...

, maritime patrol is usually aimed at identifying human activities.

Maritime patrol refers to active patrol of an area, as opposed to passive monitoring systems such as sound-detection fixtures or land-based spotters. A patrol consists of a ship, submarine, aircraft or satellite examining the patrolled area and seeking out activities to be identified and reported. Maritime patrol is critical in wartime situations for navies

Navy

A navy is the branch of a nation's armed forces principally designated for naval and amphibious warfare; namely, lake- or ocean-borne combat operations and related functions...

 to locate enemy forces to engage or defend against. Peacetime patrols are important for interdiction

Interdiction

Interdiction is a military term that refers to the act of delaying, disrupting, or destroying enemy forces or supplies en route to the battle area. A distinction is often made between strategic and tactical interdiction...

 of criminal activities and for ensuring legal use of waters.

Maritime patrols can be conducted by surface ship

Ship

Since the end of the age of sail a ship has been any large buoyant marine vessel. Ships are generally distinguished from boats based on size and cargo or passenger capacity. Ships are used on lakes, seas, and rivers for a variety of activities, such as the transport of people or goods, fishing,...

s and submarine

Submarine

A submarine is a watercraft capable of independent operation below the surface of the water. It differs from a submersible, which has more limited underwater capability...

s, by aircraft

Aircraft

An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...

 and other aerial vehicles, and even by satellite

Satellite

In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....

s. Human spotting remains an important part of detecting activity, but increasingly electronic systems are used.

Several types of maritime patrol missions exist:

• Military: Navies and air forces employ patrols to locate and identify enemy or potential enemy ships and submarines. The patrols report these findings to combat vessels which can then take appropriate action. Characteristics to identify are the numbers and types of vessels, as well as bearing and speed information to assist tracking the units. Anti-submarine patrols often deploy sonobuoy
  Sonobuoy
  A sonobuoy is a relatively small expendable sonar system that is dropped/ejected from aircraft or ships conducting anti-submarine warfare or underwater acoustic research....
  
  s or other devices to assist with tracking. During peacetime, patrols are maintained by military forces for practice and to prevent surprise deployments by enemies.

• Law enforcement: Countries with extensive coastlines are vulnerable to those entering or exiting the country undetected. In particular smuggling
  Smuggling
  Smuggling is the clandestine transportation of goods or persons, such as out of a building, into a prison, or across an international border, in violation of applicable laws or other regulations.There are various motivations to smuggle...
  
   is often carried out over water. Law enforcement agencies often employ maritime patrols to assist interception of such activities.

• Economic: Water areas, in particular those close to the coast, are areas of economic activity. Not only shipping
  Shipping
  Shipping has multiple meanings. It can be a physical process of transporting commodities and merchandise goods and cargo, by land, air, and sea. It also can describe the movement of objects by ship.Land or "ground" shipping can be by train or by truck...
  
   but also fishing
  Fishing
  Fishing is the activity of trying to catch wild fish. Fish are normally caught in the wild. Techniques for catching fish include hand gathering, spearing, netting, angling and trapping....
  
   and even tourism
  Tourism
  Tourism is travel for recreational, leisure or business purposes. The World Tourism Organization defines tourists as people "traveling to and staying in places outside their usual environment for not more than one consecutive year for leisure, business and other purposes".Tourism has become a...
  
   are important economic activities to coastal countries. Patrolling these waters falls to maritime patrols. Such patrols may seek fishing vessels which are outside of prescribed fishing grounds (often from neighboring countries' fleets) or which are not adhering to regulations. Additionally, patrols may assist customs agencies by monitoring commercial shipping traffic in controlled waters.

• Coast defence: Coast defence identifies and intercepts threats to coastal areas. This may include preventing infiltrations or discouraging enemy surveillance of coastal installations. Law enforcement patrols aim at preventing criminals from reaching the shoreline.

• Rescue: Although not necessarily a primary mission of maritime patrol assets, they are often used to assist in maritime rescue operations, both for searching and often to extract survivors too.

Maritime patrols are conducted by all manner of ships, aircraft, and other assets:

• Surface ship: The most traditional form of maritime patrol is to send out ships to sail the seas and report their findings. Generally smaller vessels with limited combat ability are employed, so that larger numbers can be acquired and thus larger expanses can be covered. Sophisticated electronics are installed to increase these units' efficiency. Despite limited armament, such vessels are usually capable of engaging enemy patrols and defending to some degree from air attack. Patrol vessels are often specialized for a certain type of mission, such as anti-submarine patrol. Surface ships are also heavily used for law enforcement.

• Submarine: Surface vessels are vulnerable to enemy naval forces, as well as to air attack. To offset this, submarines came into use as patrol vessels for missions farther from home waters. Submarines also carry torpedoes which allowed them to exploit opportunity targets better than most other patrols. Unfortunately, their limited sensors above the surface cut down on the amount of surface they can cover at any given time. Submarines are generally only used for military patrol missions.

• Aircraft: Patrol was one of the first roles for aircraft at sea, with larger ships equipped with small planes for use as scouts. Generally aircraft carried by ships are used for patrol of the waters around the ship to prevent enemy ships and submarines from getting near. Carriers use such patrols to identify targets for air strikes. Larger land-based aircraft are capable of patrolling for long distances and maintaining their patrols for many hours. However, aircraft are limited in the amount of armaments they carry, instead relying on airstrikes by other planes to attack targets. Due to their high point of view and fast speed, aircraft can cover large expanses of water quickly. Anti-submarine patrol is a common task for maritime patrol aircraft.

• Helicopter: Helicopters have an ability to hover which allows them to scan the surface and to drop sensors into the water to search underwater. Their small size and lack of need for landing space also makes them ideal for employment on ships. However, helicopters have limited range, and cannot maintain long endurance patrols like land-based aircraft. Helicopters are heavily employed in law enforcement patrols.

• Satellite: The value of satellites for maritime patrol was quickly grasped as a satellite has the ability to monitor any patch of water immune to enemy attack. Sensors can identify activities on the surface and underwater. Limitations exist: satellites may not be in proper position when needed, or a country may simply lack enough to cover the desired areas. They are very expensive and only a few nations can afford sufficient coverage. Additionally they are subject to interference both by weather patterns and by human countermeasures.