[1][2] Before World War II, Kosacki was a technician in the Artillery Department of the Polish Ministry of National Defense.

Shortly before the war, he joined the clandestine Special Signals Unit, a secret institute that worked on electronic appliances for the army.

Following the 1939 invasion of Poland, he managed to get to the United Kingdom, where he continued his service in the Polish Army as a signals officer.

For many years he held the chair in electronics at the Institute for Nuclear Research at Otwock - Świerk.

During World War II, Kosacki's name was classified in order to protect his family, which had remained behind in German-held Poland.