In warfare, infiltration tactics involve small, lightly equipped infantry forces attacking enemy rear areas while bypassing enemy front line strongpoints and isolating them for attack by follow-up troops with heavier weapons.
Development during World War I
These tactics emerged gradually during the later years of World War I, used in various forms by the Russian general Aleksei Brusilov in the Brusilov Offensive of 1916, by the British Third Army at the Battle of Arras in April 1917 (most notably the capture of Vimy Ridge by the Canadian Corps), following the reorganisation of British infantry platoons according to the new Manual SS 143, in the new year and by the German military in the Siege of Riga in September 1917 and the Battle of Caporetto in October 1917.
The tactics became especially associated with the stormtroopers of the German Army, and were also called Hutier tactics, after General Oskar von Hutier, who used these tactics to great effect during Operation Michael in March 1918.
A form of infiltration tactics was proposed by French headquarters on 16 April 1915 in Note 5779, which stated that the first waves of infantry should penetrate as far as possible and leave enemy strongpoints to be dealt with by follow-up waves. These were partially adopted on 9 May 1915, the opening day of the Second Battle of Artois, by the French XXXIII Corps which advanced 4.5km in the first hour and a half of the attack. The problem was reinforcing and holding the gains against German counterattack. 
A young French infantry officer, Captain André Laffargue, put forward similar ideas in a pamphlet written in August 1915 Étude sur l’attaque dans la période actuelle de la guerre (Study of the attack in the current period of the war). Laffargue based his proposals in particular on his experiences attacking immediately south of Neuville-Saint-Vaast on 9 May 1915 when commanding a company of 153rd Infantry Regiment. Laffargue was left wounded on the German front line but his Regiment advanced another 1.5 km, only to be held up by two German machine guns. Laffargue's pamphlet focused primarily on the small-unit perspective, calling for mobile firepower to deal with local resistance such as machine guns and advocating that the first waves of an attack advanced in the intervals or gaps between centres of resistance which should be temporarily neutralised on the edges by fire or heavy smoke. They would then be encircled and dealt with by successive waves. Had these methods been followed Laffargue suggests that the attack could have resulted in a complete breakthrough of the German defences and the capture of Vimy Ridge.
The crucial distinction between the forms of infiltration advocated by French headquarters and Laffargue as against those under development in the German army was that the French remained firmly wedded to the use of the attack by waves, despite the high casualties which could ensue. Laffargue put forward the view that the psychological support of the attack in line was necessary to enable men to advance against heavy fire. The French Army published Laffargue's pamphlet in 1915 (having already put forward a more developed version of his ideas in Note 5779) and the following year a commercial edition found wide circulation. The British, like all combatants during 1914-18, made frequent use of wave attacks and translated and published Laffargue's pamphlet in December 1915. The US Infantry Journal published a translation as The Attack in Trench Warfare in 1916. 
The claim that the Germans translated and used Laffargue's pamphlet as a training manual has been refuted by Gudmundsson. The Germans were already developing their own form of infiltration tactics: an experimental Pioneer unit commanded by a Major Caslow, and later Hauptmann Willie Rohr had been formed in the spring of 1915, over two months before Laffargue's pamphlet was published. (Rohr was promoted to Major after assuming command of the experimental unit.) 
Named for the German general of the infantry Oskar von Hutier. Infiltration attacks began with brief and violent bombardments of the enemy front lines, to suppress and demoralize enemy combatants stationed there. The bombardment also targeted enemy rear areas to destroy or disrupt roads, artillery, and command units.
This was done to confuse the enemy, and reduce their capability to launch effective counterattacks from secondary defense lines. For maximum effect, the exact points of attack remained concealed until the last possible moment.
Light infantry led these attacks. They would attempt to penetrate enemy weak points to bypass and isolate heavily defended positions in the front line. Infantrymen with heavier weapons would then follow-up and have a great advantage when attacking the isolated enemy strong points. Other reinforcements would then enter these breaches, and the entire enemy line would shortly collapse. The attacks relied heavily on speed and surprise.
This tactic initially worked well and saw heavy use. However, because of this extensive implementation, the enemy quickly developed effective defenses. Also, as in the case of the more traditional mass attack, reserve troops following the assault units had to consolidate any gains against an enemy counterattack.
One of the problems of World War I was that even when a breakthrough was made, the ground was so devastated that moving up reserves and material was difficult, allowing the enemy time to regroup. Thus, even with the new tactics and their relatively light use of artillery, attacks would tend to bog down sooner or later, and no massive breakthrough was possible.
Dien Bien Phu
At the Battle of Dien Bien Phu, Major Marcel Bigeard, commander of the French 6th Colonial Parachute Battalion (6th BPC), used infiltration tactics in an attempt to defend the besieged garrison against the Viet Minh trench warfare tactics. Bigeard's parachute assault companies were supported by concentrated artillery and air support, and received help from tanks, allowing two companies (1st under Lieutenant René Le Page and 2nd under Lieutenant Hervé Trapp) numbering no more than 180 men to recapture the important hilltop position of Eliane 1 from a full Viet Minh battalion, on the early morning of 10 April 1954.
Other parachute battalion and company commanders also used similar tactics during the battle.
- Kraus Podcast. Kraus, Early trench tactics in the French Army, pp. 23-32.
- Jones, Infiltration by Close Order
- CDS 333 A Study of the Attack in the Present Phase of War: Impressions and Reflections of a Company Commander (December 1915) http://www.birmingham.ac.uk/Documents/college-artslaw/war/List-of-SS-Pamphlets.doc
- Laffargue The Attack in Trench Warfare.
- Gudmundsson, Stormtroop Tactics, pp. 193-196.
- Samuels, Martin Doctrine and Dogma, passim
- Samuels, Martin Command or Control?, passim
- Stormtroop Tactics, Appendix C and passim
- Samuels, Martin Doctrine and Dogma, 55
- Davidson, Vietnam at War, p. 265.
- Davidson, Phillip B. Vietnam at War: The History, 1946–1975. New York: Oxford University Press, 1991. ISBN 0-19-506792-4, ISBN 0-89141-306-5.
- Gudmundsson, Bruce I. Stormtroop Tactics: Innovation in the German Army, 1914–1918. New York: Praeger, 1989. ISBN 0-275-93328-8.
- Simon Jones, Infiltration by Close Order: André Laffargue and the Attack of 9 May 1915.
- Kraus, Jonathan. Early trench tactics in the French Army: the Second battle of Artois May-June 1915. Farnham: Ashgate, 2013. ISBN 978-1-4094-5500-4.
- Kraus, Jonathan. Podcast: The Second Battle of Artois, May 1915: the new turning-point.
- Laffargue, André. The Attack in Trench Warfare Impressions and Reflections of a Company Commander by Capt. André Laffargue 153rd Infantry, French Army, Translated for the Infantry Journal by an Officer of Infantry. Washington: The United States Infantry Association, 1916. https://archive.org/details/attackintrenchwa00laff.
- Samuels, Martin. Doctrine and dogma: German and British infantry tactics in the First World War. New York: Greenwood Press, 1992. ISBN 0-313-27959-4.
- Samuels, Martin. Command or control?: Command, training, and tactics in the British and German armies, 1888–1918. London; Portland, Oregon: Frank Cass, 1995. ISBN 0-7146-4570-2, ISBN 0-7146-4214-2.
- House, Jonathan M. Toward Combined Arms Warfare: A Survey of 20th-Century Tactics, Doctrine, and Organization. U.S. Army Command General Staff College, 1984. Available online (5 February 2005) or through University Press of the Pacific (Honolulu, Hawaii, 2002). ISBN 1-4102-0159-7.
- Pope, Stephen, Elizabeth-Anne Wheal, and Keith Robbins, eds. The Macmillan Dictionary of the First World War. London: Macmillan Reference Books, 1995. ISBN 0-333-61822-X.