He was enlisted in the army when the war broke out, was captured in 1940 and interned by the Germans, but escaped and made his way back to France in July 1941.

Back in France he organized the founding congress of the French Union of Agricultural Youth and the Popular Front in the Ain.

After hearing of the German attack on Russia, on the night of 25–26 July 1941 Ouzoulias and two companions escaped and hid on a train bound for France.

[3] At this time the JC was mainly involved in propaganda, publishing tracts and clandestine newspapers, with minimal armed action.

At a session in 15–17 August it was agreed that members of the JC should receive weapons training and should increase sabotage and attacks on occupation troops.

The FTP unified three Communist organizations, the Bataillons de la Jeunesse, the Organisation Spéciale and the Main d’oeuvre immigrée.

This resulted in Belbéoch joining the commissariat of the 12th arrondissement of Paris, in which position he could help members of the Resistance to gain false papers, and could help persecuted Jews.

[4] Ouzoulias was a proponent of quick strikes against carefully studied targets by small groups of fighters, who would then rapidly withdraw.

He also drew up guidelines for urban warfare in which FTP units could attack greatly superior German forces and be protected while they withdrew.

She immediately went into hiding, and on 26 October 1943 gave birth to son, who was registered as Marc Hubert, "born of unknown parents."

[4] Five days after the surrender of Dietrich von Choltitz, the German governor of Paris, Ouzoulias assigned Pierre Georges the task of forming a battalion of resistance fighters.

The column was to form the nucleus of a Free French force in Lorraine, which would be joined by volunteers from Paris and the eastern regions of France as soon as possible.

[7] In the autumn of 1944, Ouzoulias was charged by de Gaulle with integrating the FTP members with the regular French army.

[3] Ouzoulias wrote about the young communists who participated in the armed resistance in his 1967 Les Bataillons de la Jeunesse.