A combatant ship is a naval ship

Naval ship

A naval ship is a ship used for combat purposes, commonly by a navy. Naval ships are differentiated from civilian ships by construction and purpose...

 designed primarily to go "into harm's way."

A combatant ship is armed with offensive weaponry, although the ship and its weapons may be employed in offensive or defensive roles. Combatant ships and auxiliary ship

Auxiliary ship

An auxiliary ship is a naval ship which is designed to operate in any number of roles supporting combatant ships and other naval operations. Auxiliaries are not primary combatants, although they may have some limited combat capacity, usually of a self defensive nature.Auxiliaries are extremely...

s form the two primary groups of naval vessels. The key discriminator is that, if even armed, auxiliary ship weapons are used for ship self defense only.

Combatant ship operations include: anti-ship warfare, also known as surface warfare

Surface warfare

Modern naval warfare is divided into three operational areas: surface warfare, air warfare and submarine warfare. Each area comprises specialized platforms and strategies used to exploit tactical advantages unique and inherent to that area....

; air warfare; anti-air warfare; anti-submarine warfare

Anti-submarine warfare

Anti-submarine warfare is a branch of naval warfare that uses surface warships, aircraft, or other submarines to find, track and deter, damage or destroy enemy submarines....

; amphibious assault; and land attack.

Types

• Aircraft carrier
  Aircraft carrier
  An aircraft carrier is a warship designed with a primary mission of deploying and recovering aircraft, acting as a seagoing airbase. Aircraft carriers thus allow a naval force to project air power worldwide without having to depend on local bases for staging aircraft operations...
  
  s
• Battleship
  Battleship
  A battleship is a large armored warship with a main battery consisting of heavy caliber guns. Battleships were larger, better armed and armored than cruisers and destroyers. As the largest armed ships in a fleet, battleships were used to attain command of the sea and represented the apex of a...
  
  s, cruiser
  Cruiser
  A cruiser is a type of warship. The term has been in use for several hundreds of years, and has had different meanings throughout this period...
  
  s, destroyer
  Destroyer
  In naval terminology, a destroyer is a fast and maneuverable yet long-endurance warship intended to escort larger vessels in a fleet, convoy or battle group and defend them against smaller, powerful, short-range attackers. Destroyers, originally called torpedo-boat destroyers in 1892, evolved from...
  
  s, frigate
  Frigate
  A frigate is any of several types of warship, the term having been used for ships of various sizes and roles over the last few centuries.In the 17th century, the term was used for any warship built for speed and maneuverability, the description often used being "frigate-built"...
  
  s, corvette
  Corvette
  A corvette is a small, maneuverable, lightly armed warship, originally smaller than a frigate and larger than a coastal patrol craft or fast attack craft , although many recent designs resemble frigates in size and role...
  
  s
• Fast attack craft
  Fast Attack Craft
  Fast Attack Craft are small, fast, agile and offensive warships, that are armed with anti-ship missiles, guns or torpedoes. These are usually operated in close proximity to land as they lack both the sea-keeping and all-round defensive capabilities to survive in blue water. The size of the vessel...
  
  
• 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
• Amphibious assault ship
  Amphibious assault ship
  An amphibious assault ship is a type of amphibious warfare ship employed to land and support ground forces on enemy territory by an amphibious assault...
  
  s
• Patrol craft

Most types perform many of the combatant operations, see their respective articles for details.

Combatant vs. auxiliary roles

The roles of combatant and auxiliary ships can overlap. An aircraft carrier's roles start with the traditional auxiliary roles of transport (of aircraft) and replenishment (of her battle group), but the ability to launch her aircraft for offensive strikes or defensive air cover makes her a prime combatant. The difference between a combatant amphibious assault ship and an auxiliary troop ship, both of which carry troops, is the organic ability to land the troops under combat conditions with landing craft

Landing craft

Landing craft are boats and seagoing vessels used to convey a landing force from the sea to the shore during an amphibious assault. Most renowned are those used to storm the beaches of Normandy, the Mediterranean, and many Pacific islands during WWII...

 or helicopter

Helicopter

A helicopter is a type of rotorcraft in which lift and thrust are supplied by one or more engine-driven rotors. This allows the helicopter to take off and land vertically, to hover, and to fly forwards, backwards, and laterally...

s. Unarmed supply, research, and rescue submarines are properly auxiliaries.