In 1924 he joined the Warszawianka sports club, where he started training in a variety of disciplines, including swimming, running and football.
After graduating from the reserve NCO school in Zambrów, Lokajski joined the Central Sport Education Centre in Bielany, Warsaw.
After his brother, Józef Lokajski, was killed by the Germans, Eugeniusz took over his duties in the Armia Krajowa unit, where he started serving as the person responsible for arms and munitions transport.
After the outbreak of the Warsaw Uprising, both Lokajski and his sister joined the Koszta company, the staff defense unit defending the commanders of the Śródmieście area.
After the action, Lokajski's unit was withdrawn to the rear and became the tactical reserve of the HQ, used for filling the gaps in Polish lines.
Among the most serious fights he took part in was the struggle for the barricades on Chmielna street, as well as for the Main Post Office, in which he managed to retake the lost building and capture 18 German prisoners of war.
Although his unit was decimated and cut out in the ruins without supplies, food and ammunition, Lokajski held out with his men until a relief force arrived – 48 hours later.
His main task was to prepare photos of important AK soldiers for fake German documents, which would allow them to evade captivity and continue the struggle.