During the Czech mobilisation campaign in September 1938, Josef Vlach engaged in the activities of the National Shooting Union. Armed with a rifle, he patrolled bridges located near Pilsen and guarded them against the Sudeten Germans. As a student he attended the funeral of Jan Opletal, which took place on 15 November 1939. Two days later, on 17 November, he was arrested by the Gestapo in Hlávka Dormitory and transported to Sachsenhausen concentration camp, where he was held prisoner till June 1940.

Josef Vlach spent the end of the war in his hometown of Pilsen, where he met many American soldiers. He truly appreciated the approach of their commissioned officers, who proudly served as examples to common soldiers. The ranks of US commissioned and non-commissioned officers were marked by stripes on the rear side of the helmet. Therefore, the rank insignia was visible only if the officer moved ahead of his troops.

Witnesses often remember American soldiers for their generosity and love affairs with Czech women. Though Mr. Vlach points out that an often ignored aspect of their life was their devoutness. "It was fantastic to watch American soldiers attending mass in the Redemptorist Church on the first Sunday after May 5th, 1945. They still had their helmets and rifles. While kneeling, they were holding the rifles, the helmets placed close to them. They brought their own chaplains, who were recognisable only by a tiny cross.”

After the war, he finished his university studies and pursued a career in science. Until 1983 he worked at the Energy Research Institute, later at the Research Institute of Fuel and Energy Complex, and gave lectures at the Czech Technical University.