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A Long-range penetration patrol, group, or force is a special forces operations unit able to remain in and move long distances behind enemy lines far away from direct contact with friendly forces as opposed to Long Range Reconnaissance Patrol, a small group primarily engaged in scouting missions. For recent doctrine, see special reconnaissance and the Battle of Signal Hill Vietnam for a direct action reconnaissance-in-force.
Though the concept of long range penetration is as old as war itself, in the modern era it is recognised as starting with Major Ralph Alger Bagnold with his 1940 Long Range Desert Group (LRDG) in the Western Desert and Orde Wingate with his Chindits in Burma in World War II. The LRDG carried out operations of reconnaissance and sabotage far behind the enemy's lines in the Libyan Desert.
Major Bagnold was an experienced desert explorer who had his LRDG trained in desert driving, navigation through using the sun and stars as well as a compass, and knowing their territory. They were supplied by all the equipment that their trucks could carry.
Brigadier Orde Wingate, a professional soldier with eccentric behaviour created and led guerrilla units in Palestine and Ethiopia before being transferred to Burma in 1942. Wingate had ideas of deep penetration operations that could be made possible through improvements in the range of communication devices and airborne supply by long range aircraft. At the Quebec Conference in 1943, Wingate explained his ideas to Winston Churchill, Franklin D. Roosevelt, and many other leaders. Wingate proposed creating strongholds in enemy territory that would be supplied by air and be as effective against the enemy as conventional troops.
Brigadier Wingate was given command of the 77th Indian Infantry Brigade that acquired the name of Chindit from a suggestion by Captain Aung Thin of the Burma Rifles. The name was a corruption of the mythical beast that guards Buddhist temples called 'Chinthé' or 'Chinthay'. The unit was supported by the United States Army Air Forces 1st Air Commando Group and carried out two major operations. The first was entering Burma on a 200 mile mission in February 1943 with 3,000 troops, with mules and some elephants for the carrying of supplies. Wingate thought the operation a success, but Field Marshal William Slim thought the operation a failure.
Inspired by the Quebec Conference and keeping in mind General Joseph Stilwell's requests for American infantry to support his Chinese troops in the China Burma India Theatre of World War II, General George Marshall sent a telegram to Stilwell notifiying him that America would organise their own Long Range Penetration Force made up of three groups, one from jungle warfare trained troops who were no longer required in Panama, the second from jungle warfare trained troops from Continental American army bases, and the third, experienced jungle fighters from the South Pacific (Admiral Chester Nimitz's troops who had fought on Guadalcanal and the Solomon Islands) and (General Douglas MacArthur's troops who had fought in New Guinea). The unit was renamed the 5307th Composite Unit (Provisional) but more popularly known as Merrill's Marauders and carried out operations in Burma in 1944.
Post World War II 
After World War II, long range penetration operations were primarily conducted by small units of men often varying in size from five to thirty men. Sabotage, surveillance, and seizure of strategic locations were the primary objective carried out deep behind enemy lines. Most notable are the British Special Air Service (SAS), the Australian Special Air Service Regiment, the New Zealand Special Air Service (NZSAS), the Rhodesian Special Air Service, the South African's 32nd Battalion operations after the Angolan Civil War, and the Sri Lanka Army long range penetration units operations during the Sri Lankan Civil War.
Vietnam War 
In April 1968 members of the 2nd Platoon, Company E, 52nd Infantry, 1st Air Cavalry Division, Long Range Reconnaissance Patrol (LRP), commanded by Captain Michael Gooding and Lieutenant Joseph Dilger, conducted one of the most daring long-range penetration operations of the Vietnam War when they seized the strategic 4,879-foot mountain peak of Dong Re Lao Mountain, dubbed "Signal Hill" by headquarters during Operation Delaware. Signal Hill, was deep in enemy territory in the heavily fortified A Shau Valley. After intense fighting against troops of the North Vietnamese Army, the mountaintop was secured, providing a vital communications relay site and fire support base for massive air assault operations to proceed in the valley by the 1st and 3rd Brigades, 1st Air Cavalry Division. Since satellite communications were a thing of the future, those brigades, hidden deep behind the towering wall of mountains would have been unable to communicate to their headquarters at Camp Evans near the coast or to approaching aircraft. 
- Lurps: A Ranger's Diary of Tet, Khe Sanh, A Shau, and Quang Tri, revised ed. Rowman & Littlefield Publishing Group, Landham, MD (2009).
- Photographic history of 1st Air Cavalry Division Lurp / Rangers in Vietnam 1968.
See also 
- Battle of Signal Hill Vietnam
- Company E, 52nd Infantry (LRP)
- Dong Re Lao Mountain
- Long Range Reconnaissance Patrol
- Long Range Surveillance Detachment
- Robert C. Ankony, Lurps: A Ranger's Diary of Tet, Khe Sanh, A Shau, and Quang Tri, revised ed., Rowman & Littlefield Publishing Group, Lanham, MD (2009).
- Ogburn Jr, Charlton The Marauders (1956)
- James N. Rosenau, Subversion and Insurgency, Rand Publishing, (2006).
- Robert C. Ankony, "No Peace in the Valley," Vietnam magazine, Oct. 2008,26-31