ORIGINAL: dwg
Anywhere you see 'groupement de marche' (gm) the best translation is probably 'battlegroup', you may also also see Bataillon de Marche, Regiment de Marche and Division de Marche, which are all basically units formed from other units for a specific campaign, the type of unit will go in the middle, so you might get a Bataillon d'Infanteries de Marche (which would be a BIM).
Just to elaborate on that, the term "de marche" is used in a number of cases :
- for temporary units made out of unaffected troops, usually out of depot or just mobilised, marching to the front where they would be dispatched to regular units, this is the original meaning
- for the reverse situation, units marching back from the front to depots, usually remnants of units
- then for adhoc units incorporating elements detached from various parents, this was typical in colonial and foreign expeditions, where one would assemble a régiment de marche from a collection of battalions taken from colonial units in the area. This was the case in Indochina
- then again, for any unit used out of its original command : for instance, during WWI, many battaillons d'infanterie légère d'afrique (aka bat' d'af, units which conscripted former convicted felons), were detached to the West front, and just changed their name to BMILA (bataillon de marche d'infanterie légère d'Afrique). A similar situation happened after Sedan, in 1870, when colonial troops were called in, and formed Zouaves de marche, chasseurs de marche, in the infamous Bourbaki army.
During WWII, the last case happened with the Régiment de marche du Tchad, which used to be Régiment de tirailleurs sénégalais du Tchad, but was renamed to indicate the change of command, and the incorporation of (a small number of) volunteers from the free french. The régiment de marche du Tchad became the first free french regiment, and was allowed to keep its "de marche" afterwards (it is still named that, even though it is not a temporary force)
I believe other Free French regiments originally from the Armée d'Afrique (loyal to Vichy until 43) added "de marche" to their name to stress their difference (but most reverted to their original names later)
Another famous gotcha is the 3e REI, which took back the name Régiment de marche de la Légion Etrangère from 43 to 45. The RMLE had been created during WWI to incorporate several battalions of the FFL (which belonged to Armée d'Afrique) fighting in France. After the war, the unit was kept and renamed the 3e REI. In 1942, after Torch, it became the 3eREIM régiment étranger d'infanterie de marche, and then took back its former name as RMLE.
But in general, "de marche" more or less means "provisional".
Francois