French Forces of the Interior The French Forces of the Interior ( ) refers to French resistance fighters in the later stages of World War II . Charles de Gaulle used it as a formal name for the resistance fighters . The change in designation of these groups to FFI occurred as France ' s status changed from that of an occupied nation to one of a nation being liberated by the Allied armies . As regions of France were liberated , the FFI were more formally organized into light infantry units and served as a valuable manpower addition to regular French forces . In this role , the FFI units manned less active areas of the front lines , allowing regular French army units to practice economy of force measures and mass their troops in decisive areas of the front . Finally , from October 1944 and with the greater part of France liberated , the FFI units were amalgamated into the French regular forces , thus ending the era of the French irregulars in World War II . Liberation . After the invasion of Normandy in June 1944 , at the request of the French Committee of National Liberation , SHAEF placed about 200 , 000 resistance fighters under command of General Marie Pierre Koenig , who attempted to unify resistance efforts against the Germans . General Eisenhower confirmed Koenig ' s command of the FFI on 23 June 1944 . The FFI were mostly composed of resistance fighters who used their own weapons , although many FFI units included former French soldiers . They used civilian clothing and wore an armband with the letters " F . F . I . " According to General Patton , the rapid advance of his army through France would have been impossible without the fighting aid of the FFI . General Patch estimated that from the time of the Mediterranean landings to the arrival of U . S . troops at Dijon , the help given to the operations by the FFI was equivalent to four full divisions . FFI units seized bridges , began the liberation of villages and towns as Allied units neared , and collected intelligence on German units in the areas entered by the Allied forces , easing the Allied advance through France in August 1944 . According to a volume of the U . S . official history of the war , In Brittany , southern France , and the area of the Loire and Paris , French Resistance forces greatly aided the pursuit to the Seine in August . Specifically , they supported the Third Army in Brittany and the Seventh U . S . and First French Armies in the southern beachhead and the Rhône valley . In the advance to the Seine , the French Forces of the Interior helped protect the southern flank of the Third Army by interfering with enemy railroad and highway movements and enemy telecommunications , by developing open resistance on as wide a scale as possible , by providing tactical intelligence , by preserving installations of value to the Allied forces , and by mopping up bypassed enemy positions . Political tension . On 20 June 1944 , the French high command decreed the mobilization requirements dating from the start of the war were still in effect , that the FFI units were to be made part of the French Army , and that the FFI was subject to French military law . Assuming control of the French national government after the liberation of Paris , Charles de Gaulle was almost immediately confronted with a challenge to his authority by an FFI flush with triumph as towns and cities were liberated in the wake of the German retreat from France . In late August 1944 , there were incidents of FFI misbehavior in the region of Paris , highlighting the risks of having an armed and organized citizenry that suddenly found itself without a mission . De Gaulle believed France required a single decisive leader to restore effective government . The FFI believed they should have a share in national power because of their contribution to the Allied war effort . Subsequently , de Gaulle declared the FFI would be either disbanded or integrated into the French Army , and a series of tense meetings between de Gaulle and FFI leaders in major cities ensued . Despite FFI disenchantment with de Gaulle ' s methods , in large part they accepted his decision that FFI members would either be amalgamated into the French regular army or return to civilian life . Amalgamation . Subsequent to the liberation of areas where FFI units operated , they often formed battalions and brigades named for their commanders or region of origin ( Battalion Oziol , etc . ) These FFI units were predominantly of the light infantry class , although some formed light reconnaissance units like the 12th Regiment of Dragoons . Some of these units were used to besiege German troops in still - occupied French ports or to secure France ' s alpine frontier with Italy , others were used to secure Allied lines of communications in France , and still others were assigned as army reserve units for the use of General de Lattre de Tassigny ' s French First Army . From October 1944 until March 1945 , the FFI units were amalgamated into the French Army in order to regularize the units . Units such as the 49th Infantry Regiment ( formerly the FFI Corps Franc Pommiés ) and the 3rd Demi - Brigade of Chasseurs ( formerly the FFI Alsace - Lorraine Brigade ) were constituted in this manner using FFI manpower . Amalgamation was successful in varying degree ; the training , tactics and attitudes of the former French Resistance fighters often differed from those of the regular soldiers with whom they served . General De Lattre ' s comments on this situation are enlightening : [ Traditional military values ] were not and could not be the characteristics of the F . F . I . units . Condemned to be born and live in secret , placed outside the law by the enemy and by the enemy ' s accomplices , they had above all developed the revolutionary military virtues , those of partisans . By force of circumstances the personalities of the leaders had played a determining role and had stamped each maquis with a different brand . To the regiments we had landed the extreme variety of the F . F . I . organizations , their at least peculiar discipline , the differing quality of their groups , the poverty of their equipment , the crying inadequacy of their armament and supplies , the heterogeneity of their officering , the facility with which their superior ranks had been assigned , and in certain cases the ostensibly political nature of their aims , ran counter to the classical military outlook of many officers , some of whom , in reaction , exaggerated their regulation strictness . The part [ the FFI ] had taken in the fight for liberation not only encouraged them rightly in the wish to retain their individuality ; their successes , valued often from a local angle , established in their view the excellence of the military system which circumstances had led them to create and which they intended to substitute for the traditional system , which they considered out - of - date . A total of 68 infantry regiments and half - brigades , two special forces battalions , 20 light infantry or reconnaissance battalions , one tank battalion , sixteen artillery regiments , two anti - aircraft artillery regiments , five engineer regiments , and three construction regiments were ultimately formed from FFI manpower by the close of 1945 . Weapons and equipment . The weapons and equipment of the FFI were highly varied . Because they were not units that the United States had formally agreed to logistically support , they were not eligible to receive the standard U . S . equipment that was provided to French regular army units . Thus , the FFI units often clothed themselves in nonstandard uniforms or uniforms of 1940 vintage . The same condition existed with weapons , with the use of captured German infantry weapons a common practice . Because of the mix of American , British , French , German , and other weapons , the supply of ammunition and spare parts was complicated and often difficult to accomplish . By no means unique in the diversity of its armament , the 34th Infantry Regiment ( formed on 1 January 1945 ) possessed the following weapons in August 1945 : 1 , 760 ( German ) Mauser rifles , 470 ( British ) Sten sub - machine guns , 108 German sub - machine guns , 27 ( French ) Hotchkiss machine guns , 33 50 - mm mortars and 12 81 - mm mortars , two 20 - mm cannon , and three 25 - mm cannon . The soldiers ' uniforms were described as second - hand and of diverse origins . Some heavy armored fighting vehicles were obtained , notably British Cromwell tanks ( 150 provided by Great Britain ) and captured German tanks ( 44 , of which 12 were Panthers ) . The 12th Regiment of Dragoons received 12 Cavalier tank s among other British equipment in April 1945 . In other cases , FFI units used vehicles no longer favored by Allied forces , such as the U . S . M6 Fargo , a light truck with a portee 37 mm antitank gun . Finally , civilian vehicles and practically anything else in running condition were pressed into service and used until they could no longer be maintained . French strategic asset . As regions of France were liberated , the FFI provided a ready pool of semi - trained manpower with which France could rebuild the French Army . Estimated to have a strength of 100 , 000 in June 1944 , the strength of the FFI grew rapidly , doubling by July 1944 , and reaching 400 , 000 by October 1944 . Although the amalgamation of the FFI was in some cases fraught with political difficulty , it was ultimately successful and allowed France to re - establish a reasonably large army of 1 . 3 million men by VE Day .