L.I.N.E. (Linear Infighting Neural Override Engagement) is a close quarters combat system used by the United States Marine Corps between 1989 and 1998, and then the US Army Special Forces from 1998 through to 2007. The system was developed by now retired combat-arms Marine Ron Donvito, derived from various traditional martial arts.

LINE is a highly standardized system. It is emphasized that instructors precisely stick to the curriculum. Techniques are taught using "isms" which are short phrases which describe the moves. When demonstrating a technique, instructors will call out the move's "ism" which is then repeated back by the soldiers. Soldiers then practice in a synchronized manner, shouting out the "ism" for whatever technique they are working on.

Per the US Marines Close-Quarters Combat Manual the system is broken down into six parts:

LINE I - Wristlocks and counters against chokes. 

LINE II - Counters against punches and kicks.

LINE III - Unarmed defense against the knife.

LINE IV - Knife fighting. 

LINE V - Removal of enemy personnel.
LINE VI - Unarmed defense against a bayonet attack.

In a 2007 interview with Ron Donvito in Fight Times, he presents a slightly different version of the system which is likely due to updates, removing the 'unarmed defense against a bayonet' LINE and adding a LINE for 'ground fighting.'

Fight Times: Ron Donvito and the L.I.N.E. System
Fightland: LINE and MCMAP: The Martial Arts of the US Marine Corps
US Marines Close-Quarters Combat Manual
Bullshido: Donvito's Academy of Martial Arts