'Frühling' was a German operation against the French resistance forces of the Maquis de l’Ain et du Haut-Jura based in the Gex and Oyonnax areas of the Vercors massif in the Jura mountain region of the south-eastern part of German-occupied France (7/18 April 1944).
Early in April it became clear to the resistance forces in these areas that the Germans were on the verge of starting a major effort against them. Resistance confidence remained high, however, as with the melting of the winter snow it would be difficult for the Germans to trace and locate the units of what had become, in the preceding month, the Forces Françaises de l’Intérieur (French forces of the interior): the emergence of leaves on bushes and trees made concealment easier, and the advent of more clement weather made it feasible for the French units to camp outside the forest region which had been their winter base.
The German offensive began on 7 April in the area of Oyonnax, in the south of the département of Jura and the north of the département of Ain. The Germans deployed some 4,000 men of the Sicherheitspolizei and Generalleutnant Karl Pflaum’s 157th Reserve-Division, the latter contributing four battalions of the 296th Gerbirgsjägerregiment and 297th Gerbirgsjägerregiment, the 1057th Panzerjägerabteilung, one Flak battalion, and the divisional supply, transport and medical detachments.
As the German operation began, Lieutenant Paul Vanssay was in Oyonnax to met his commander, Noël Perrotot, who could not get to the meeting as Oyonnax was surrounded by the Germans. Even so, Vanssay was able to escape the German encirclement with the aid of a local guide and reach a safe house at Buclaloup isolated in the Forêt de Champfrommier in the Combe d’Evuaz. Here a family named Grenard ran the establishment as a refuge for resistance fighters and persons who had escaped when the Germans burned the farm at Pré-Carré on the Hotonnes plateau during February.
The maquis plan remained unaltered, and therefore took the form of avoiding open combat with the Germans and instead undertaking sabotage and ambush operations. To reduce the chances of a German ambush, which could well have cost the maquis dearly, the maquis decided that the camps of its northern group, under Perrotot’s command, should be dispersed, and the pace of the German advances slowed by sabotage of the local railway lines during every night.
In Bourg en Bresse the maquis attacked the Thol barracks as a diversion that might serve to persuade the Germans that the maquis was present in some numbers right across the Ain département, especially in the areas of Bugey, Bresse and Dombes despite the fact that the Germans were concentrating on the mountains of the Bugey areas.
'Frühling' also included an attack by the Vichy French Milice Française paramilitary militia on the village of Vassieux, where it burned several farms, and either shot or deported some of the inhabitants, but the local population nonetheless maintained its support for the resistance.