1939 : Enlisted on August 26th he fights in the "drôle de guerre" in the 101st infantry regiment, where he produces some drawings too.

1940 : The 10 May, his regiment faces the German army at Chateau-Thierry.

He distinguishes himself during the battle, for which he is awarded the War Cross, Bronze Medal and the Palm.
Then it's the debacle. He is made prisoner in the Loire and is moved to the Melun camp on June 18th (1940). Sent to carry out manual labour in Saint-Saulieu in the Somme, he escapes in late August. He returns to Paris and makes himself available to the Communist Party and the Resistance.
He re-establishes contact with Jean Lurçat and Marcel Gromaire who return to Aubusson. Under an employment and home certificate issued by Lurcat, he assists him in the creation of cardboard tapestries.
Following threats by the police of Vichy, they split up for safety reasons. In fact, until this moment, he assisted in the making and distribution of clandestine papers headed by Bourdeau, which were active in the five departments of the Center of France
He then contacted the painter Menot in Cregols near Saint-Cirq-Lapopie (Lot).
In July he meets Aragon in Cahors.
He joins together with Menot, two autonomous clandestine groups for the "National Front for the fight for Liberty and Independence of France", an organisation of resistance created by the Communist Party.
He lives for a month by Raoul Dufy and then liaises with Marcel Weil in Montpellier.

13th November 1941: Boris was arrested in Cregols on a commission of the Creuse, and then brought before the session of the 13th region and sentenced to two years of imprisonment...

after being found guilty of "having produced many drawings for communist propaganda". He is sent to the detention centre in Riom in Puy de Dôme, where he stays for 17 months with 600 other ordinary prisoners (of which 32 are communist). He could only make two sketches. The penitentiary administration of the Vichy regime later acknowledges that prisoners condemned by the military court should not be sent to a civil prison.

16th July 1942 : His mother is arrested during the Vel' d'Hiv' Roundup in Paris.

She is then sent to Drancy and finally transferred to Auschwitz, where she is murdered by the Nazis.

23rd July 1943: He is transferred to the military prison of Mauzac in Dordogne and registered under number 4186.

He produces more than a hundreds of drawings that will be confiscated and lost forever.

11th November 1943 : Although he has finished his sentence, he is transferred to the camp of Saint Sulpice-la-Pointe (Tarn)

... as administrative internee on the order of the prefect, together with other communists of the Mauzac prison. He stayed there for 8 months. He becomes one the managers for the National Front for the fight for Liberty and Independence of France and the person in charge militarily for the clandestine organisation of the camp.
He decorates the walls of the camp's shacks with frescos realised from the water paint that was utilised for the maintenance of substructures.
Cf."The Saint-Sulpice's frescos"
He also produces drawings.

31st July 1944 : The SS troops invade the camp and prisoners are deported to Buchenwald.

The journey take place in cattle wagons with sealed doors.

5th August 1944 : Boris Taslitzky arrives in Buchenwald. He will be referred to as number 69022 for 9 months.

Assigned to Block 34 of the Great Camp, he becomes one of the people in charge of the direction of the party and with the protection of his comrades, he can produce more than 200 drawings. He liaises with Julien Cain, Jorge Semprun, etc.

11th April 1945 : He takes part in the camp insurrection and in its liberation.

A few days later he hands over his drawings to Christian Pineau, who was released earlier and asks him to deliver them to Aragon.

2nd May 1945 : Repatriated, he arrives in Paris.