Reconnaissance in the context of Exploratores

The first evidence of horses in warfare dates from Eurasia between 4000 and 3000 BC. A Sumerian illustration of warfare from 2500 BC depicts some type of equine pulling wagons. By 1600 BC, improved harness and chariot designs made chariot warfare common throughout the Ancient Near East, and the earliest written training manual for war horses was a guide for training chariot horses written about 1350 BC. As formal cavalry tactics replaced the chariot, so did new training methods, and by 360 BC, the Greek cavalry officer Xenophon had written an extensive treatise on horsemanship. The effectiveness of horses in battle was also revolutionized by improvements in technology, such as the invention of the saddle, the stirrup, and the horse collar.

Many different types and sizes of horses were used in war, depending on the form of warfare. The type used varied with whether the horse was being ridden or driven, and whether they were being used for reconnaissance, cavalry charges, raiding, communication, or supply. Throughout history, mules and donkeys, as well as horses played a crucial role in providing support to armies in the field.

Light cavalry comprised lightly armed and armored cavalry troops mounted on fast horses, as opposed to heavy cavalry, where the mounted riders (and sometimes the warhorses) were heavily armored. The purpose of light cavalry was primarily raiding, reconnaissance, screening, skirmishing, patrolling, and tactical communications. Prior to the 17th century they were usually armed with swords, spears, javelins, or bows, and later on with sabres, pistols, shotguns, or carbines.

Light cavalry was used infrequently by Ancient Greeks (who used hippeis such as prodromoi or sarissophoroi) and Ancient Romans (who used auxiliaries such as equites Numidarum or equites Maurorum), but were more common among the armies of Eastern Europe, North Africa, West Asia, Central Asia, and East Asia. The Arabs, Cossacks, Hungarians, Huns, Kalmycks, Mongols, Turks, Parthians, and Persians were all proficient horse archers.

Heavy cavalry was a class of cavalry intended to deliver a battlefield charge and also to act as a tactical reserve; they are also often termed shock cavalry. Although their equipment differed greatly depending on the region and historical period, heavy cavalry were generally mounted on large powerful warhorses, wore body armor, and armed with either lances, swords, maces, flails (disputed), battle axes, or war hammers; their mounts may also have been protected by barding. They were distinct from light cavalry, who were intended for raiding, reconnaissance, screening, skirmishing, patrolling, and tactical communications.

Human intelligence (HUMINT, pronounced /ˈhjuːmɪnt/ HEW-mint) is intelligence-gathering by means of human sources and interpersonal communication. It is distinct from more technical intelligence-gathering disciplines, such as signals intelligence (SIGINT), imagery intelligence (IMINT) and measurement and signature intelligence (MASINT). HUMINT can be conducted in a variety of ways, including via espionage, reconnaissance, interrogation, witness interviews, or torture. Although associated with military and intelligence agencies, HUMINT can also apply in various civilian sectors such as law enforcement.

Historically, cavalry (from the French word cavalerie, itself derived from cheval meaning "horse") are groups of soldiers or warriors who fight mounted on horseback. Until the 20th century, cavalry were the most mobile of the combat arms, operating as light cavalry in the roles of reconnaissance, screening, and skirmishing, or as heavy cavalry for decisive economy of force and shock attacks. An individual soldier in the cavalry is known by a number of designations depending on era and tactics, such as a cavalryman, horseman, trooper, cataphract, knight, drabant, hussar, uhlan, mamluk, cuirassier, lancer, dragoon, samurai or horse archer. The designation of cavalry was not usually given to any military forces that used other animals or platforms for mounts, such as chariots, camels or elephants. Infantry who moved on horseback, but dismounted to fight on foot, were known in the early 17th to the early 18th century as dragoons, a class of mounted infantry which in most armies later evolved into standard cavalry while retaining their historic designation.

Cavalry had the advantage of improved mobility, and a soldier fighting from horseback also had the advantages of greater height, speed, and inertial mass over an opponent on foot. Another element of horse mounted warfare is the psychological impact a mounted soldier can inflict on an opponent.

Light infantry refers to certain types of lightly equipped infantry throughout history. They have a more mobile or fluid function than other types of infantry, such as heavy infantry or line infantry. Historically, light infantry often fought as scouts, raiders, and skirmishers. These are loose formations that fight ahead of the main army to harass, delay, disrupt supply lines, engage the enemy's own skirmishing forces, and generally "soften up" an enemy before the main battle. Light infantrymen were also often responsible for screening the main body of a military formation.

Following World War II, the term "light infantry" has evolved to include rapid-deployment units (including commando and airborne units) that emphasize speed and mobility over armor and firepower. Some units or battalions that historically held a skirmishing role retain their designation "light infantry" for the sake of tradition.

The Pontifical Swiss Guard, also known as the Papal Swiss Guard or simply Swiss Guard, is an armed forces, guard of honour, and protective security unit, maintained by the Holy See to protect the Pope and the Apostolic Palace within the territory of the Vatican City State. Established in 1506 under Pope Julius II, it is among the oldest military units in continuous operation and is sometimes called "the world's smallest army".

The Swiss Guard is recognised by its Renaissance-era dress uniform, consisting of a tunic striped in red, dark blue, and yellow; high plumed helmet; and traditional weapons such as the halberd. Guardsmen perform their protective duties in functional attire and with modern firearms. Since the assassination attempt on Pope John Paul II in 1981, the Guard has placed greater emphasis on its nonceremonial roles and has sought more training in anti-irregular military counterintelligence, commando-style raids, counter-sniper tactics, counterterrorism, close-quarters battle, defusing and disposal of bombs, executive protection, hostage rescue, human intelligence, medical evacuation, reconnaissance, tactical driving, tactical medical services, and tactical fast shooting by small arms.

Douglas MacArthur (26 January 1880 – 5 April 1964) was an American general who served as a top commander during World War II and the Korean War, achieving the rank of General of the Army. He served with distinction in World War I; as chief of staff of the United States Army from 1930 to 1935; as Supreme Commander, Southwest Pacific Area, from 1942 to 1945 during WWII; as Supreme Commander for the Allied Powers overseeing the occupation of Japan from 1945 to 1951; and as head of the United Nations Command in the Korean War from 1950 to 1951. MacArthur was nominated for the Medal of Honor three times, and awarded it for his WWII service in the Philippines. He is one of only five people to hold the rank of General of the Army, and the only person to hold the rank of Field Marshal in the Philippine Army.

MacArthur, the son of Medal of Honor recipient Arthur MacArthur Jr., was raised on Army posts in the Old West. He was valedictorian of the West Texas Military Academy, and First Captain at the U.S. Military Academy at West Point, where he graduated first in his class in 1903. During the 1914 U.S. occupation of Veracruz, he conducted a reconnaissance mission for which he was nominated for the Medal of Honor. In 1917, he was promoted from major to colonel and became chief of staff of the 42nd (Rainbow) Division. On the Western Front during World War I, he rose to the rank of brigadier general, was again nominated for a Medal of Honor, and was awarded the Distinguished Service Cross twice and the Silver Star seven times. From 1919 to 1922, MacArthur served as Superintendent of the U.S. Military Academy, where he initiated a series of reforms. His next posting was in the Philippines, where in 1924 he was instrumental in quelling the Philippine Scout Mutiny. In 1925, MacArthur became the Army's youngest major general at the age of 45, and in 1930 was appointed Chief of Staff of the U.S. Army. He was involved in the controversial expulsion of the Bonus Army protesters in Washington, D.C., in 1932, and organized the Civilian Conservation Corps. In 1935, MacArthur was appointed Military Advisor to the Commonwealth of the Philippines. He retired from the Army in 1937, but continued as an advisor and as a Field Marshal in the Philippine Army from 1936.

A submarine (often shortened to sub) is a watercraft capable of independent operation underwater. (It differs from a submersible, which has more limited underwater capability.) The term "submarine" is also sometimes used historically or informally to refer to remotely operated vehicles and robots, or to medium-sized or smaller vessels (such as the midget submarine and the wet sub). Submarines are referred to as boats rather than ships regardless of their size.

Although experimental submarines had been built earlier, submarine design took off during the 19th century, and submarines were adopted by several navies. They were first used widely during World War I (1914–1918), and are now used in many navies, large and small. Their military uses include: attacking enemy surface ships (merchant and military) or other submarines; aircraft carrier protection; blockade running; nuclear deterrence; stealth operations in denied areas when gathering intelligence and doing reconnaissance; denying or influencing enemy movements; conventional land attacks (for example, launching a cruise missile); and covert insertion of frogmen or special forces. Their civilian uses include: marine science; salvage; exploration; and facility inspection and maintenance. Submarines can be modified for specialized functions such as search-and-rescue missions and undersea cable repair. They are also used in the tourism industry and in undersea archaeology. Modern deep-diving submarines derive from the bathyscaphe, which evolved from the diving bell.

Special operations or special ops are military activities conducted, according to NATO, by "specially designated, organized, selected, trained, and equipped forces using unconventional techniques and modes of employment." Special operations may include reconnaissance, unconventional warfare, and counterterrorism, and are typically conducted by small groups of highly trained personnel, emphasizing sufficiency, stealth, speed, and tactical coordination, commonly known as special forces (SF) or special operations forces (SOF).

ISTAR stands for intelligence, surveillance, target acquisition, and reconnaissance. In its macroscopic sense, ISTAR is a practice that links several battlefield functions together to assist a combat force in employing its sensors and managing the information they gather.

Information is collected on the battlefield through systematic observation by deployed soldiers and a variety of electronic sensors. Surveillance, target acquisition and reconnaissance are methods of obtaining this information. The information is then passed to intelligence personnel for analysis, and then to the commander and their staff for the formulation of battle plans. Intelligence is processed information that is relevant and contributes to an understanding of the ground, and of enemy dispositions and intents. Intelligence failures can happen.

World War I was the first major conflict involving the use of aircraft. Tethered observation balloons had already been employed in several wars and would be used extensively for artillery spotting. Germany employed Zeppelins for reconnaissance over the North Sea and Baltic and also for strategic bombing raids over Britain and the Eastern Front.

Airplanes were just coming into military use at the outset of the war. Initially, they were used mostly for reconnaissance. Pilots and engineers learned from experience, leading to the development of many specialized types, including fighters, bombers, and trench strafers.

Heavy infantry consisted of heavily armed and armoured infantrymen who were trained to mount frontal assaults and/or anchor the defensive center of a battle line. This differentiated them from light infantry who were relatively mobile and lightly armoured skirmisher troops intended for screening, scouting, and other tactical roles unsuited to soldiers carrying heavier loads. Heavy infantry typically made use of dense battlefield formations, such as shield wall or phalanx, multiplying their effective weight of arms with force concentration.

Heavy infantry were critical to many ancient armies, which first attested by the Sumerians in the Stele of the Vultures. It was also used by rival Assyrian and Persian Sparabara, then by Greek hoplites, Macedonian phalangites, and Roman legionaries. After the fall of Rome, heavy infantry declined in Europe but returned to dominance in the Late Middle Ages with Swiss pikemen and German Landsknechts. With the rise of firearms during early modern warfare, dense formations became increasingly infeasible, and heavy armours were either ineffective or too cumbersome to be tactically useful. By the early 18th century, heavy infantry were replaced by line infantry armed with muskets and bayonets and wearing little to no armour.

Screening is a military tactic in which a "screening force" (sometimes referred to as a "security force," or "guard force") provides early warning to a main force by using a smaller, mobile force to detect and harass an enemy's own screening and reconnaissance elements. This "screening force" hides the main body's strength and location, gathers intelligence on the enemy, and delays their advance, while avoiding decisive engagement itself. Screening may be utilized in all warfare domains; on the ground, on the sea, in the air, in space, and in cyberspace.

Patrolling is a military tactic. Small groups or individual units are deployed from a larger formation to achieve a specific objective and then return. The tactic of patrolling may be applied to ground troops, armored units, naval units, and combat aircraft. The duration of a patrol will vary from a few hours to several weeks depending on the nature of the objective and the type of units involved.

There are several different types of patrol each with a different objective. The most common is to collect information by carrying out a reconnaissance patrol. Such a patrol may try to remain clandestine and observe an enemy without themselves being detected. Other reconnaissance patrols are overt, especially those that interact with the civilian population.

A reconnaissance aircraft (colloquially, a spy plane) is a military aircraft designed or adapted to perform aerial reconnaissance with roles including collection of imagery intelligence (including using photography), signals intelligence, as well as measurement and signature intelligence. Modern technology has also enabled some aircraft and UAVs to carry out real-time surveillance in addition to general intelligence gathering.

Before the development of devices such as radar, military forces relied on reconnaissance aircraft for visual observation and scouting of enemy movement. An example is the PBY Catalina maritime patrol flying boat used by the Allies in World War II: a flight of U.S. Navy Catalinas spotted part of the Japanese fleet approaching Midway Island, beginning the Battle of Midway.

Military police (MP) are law enforcement agencies connected with, or part of, the military of a state. In wartime operations, the military police may support the main fighting force with force protection, convoy security, screening, rear reconnaissance, logistic traffic management, counterinsurgency, and detainee handling.

Army aviation is military aviation that is organized as a sub-branch under the command of an army, separate from a nation's dedicated air force. Army aviation units, sometimes described as air corps, are typically attached as a part of to a ground force and tasked to tactically assist its land warfare by providing close air support, rapid insertion, reconnaissance and logistics for front line ground operations. They usually comprise VTOL aircraft such as military helicopters, as well as gyrocopters, light fixed-wing attack aircraft and unmanned aerial vehicles (drones), and historically also aerostats such as military balloons and airships.

Prior to the establishment of separate national air forces, many armies had aviation units, which as the importance of aviation increased, were spun off into independent branches of the military. As the separation between a nation's ground and air forces led to a divergence of priorities, many armies sought to re-establish their own aviation branches to best serve their own organic tactical needs.