Key difference: The Army and the Marine Corps are two different parts of a military of a country. Army is a land based military branch is responsible for dealing with threat faced on land. In many countries, the Marines are part of the navy. However, in some countries such as the United States and the United Kingdom, the Marines are a separate department under independent command. The Marines are usually responsible for amphibious warfare and for tactical missions and support.

The Army and the Marine Corps are two different parts of a military a country. They are tasked with protecting the country again any and all threats. In the United States, these are two main branches from the five branches that is part of their military: the Army, Air Force, Navy, Marine Corps, and the Coast Guard. These branches are directly answerable to the Department of Defense, run by the Secretary of Defense. In the US, the president is the commander-in-chief of the United States Armed Forces.

The term ‘Army’ is derived from Latin word “arma” meaning “arms” or “weapons’. Army is a land based military branch is responsible for dealing with threat faced on land. This branch could also include the aviation force or air force, though in many countries this is a complete separate branch. A country usually hires full-time career soldiers who 'stand over' and do not disband during times of peace. Though a country also has reserve soldiers, which are only active during times of war or natural disasters. Some countries, like France, have labeled the term as ‘Land Army’ in order to distinguish it from the ‘Air Army’, or Air Force.

The oldest known army is the Spartan Army, where boys at the age of 7 were sent to barracks to become a soldier and could come back at the age of 30 in order to marry and have a family. At this time, the largest army in the world, by number of active troops, is the People's Liberation Army of China with 2,250,000 active troops and 800,000 reserve personnel followed by the Indian Army with 1,325,000 active troops and 2,142,821 reserve personnel. In the United States, the army is the oldest established military service in the country. Armies own equipment such as individual weapons, such as rifles, pistols; crew served weapons, such as grenades, machine guns; vehicles, such as Humvees, Tanks and uniforms. The US army is headed by a four-star general called the Army Chief of Staff, who is responsible to report to the Secretary of the Army.

Usually, the Marines are often classified as part of the navy. In many countries, the Marines are part of the navy. However, in some countries such as the United States and the United Kingdom, the Marines are a separate department under independent command. Also, some countries may classify the Marines under the army.

The Navy is armed forces that are responsible for keeping the country’s waters safe from threat. It is mainly designed for naval warfare and keeping waters free from pirates and etc. Naval warfare include anything conducted by surface ships, amphibious ships, submarines, and seaborne aviation, as well as ancillary support, communications, training, and other fields.

The Marines are usually responsible for amphibious warfare. The amphibious warfare is a type of ‘offensive military operation which uses naval ships to project ground and air military power onto a hostile or potentially hostile shore.’ The Marines’ jobs are to enter from the water and to establish a beachhead on the shore. A beachhead is a temporary line of defense which secures an area where their troops can land to begin an onslaught.

Essentially, the Marines are a mobile attack force. Their jobs are to provide tactical advantage for land and sea troops. They set up a basis for the army and navy’s missions to follow. The army, on the other hand, is the country’s primary ground-based military force. It is a vast department with various tasks that are generally aimed at running, managing and winning a war. Marines, generally have missions, which may occur during war, to win a war or to avoid circumstances leading to war. The Marine Corps is usually smaller than the army but is equally important, and in some certain situations may even be more important. 

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