After World War II broke out, Borucki went to Lviv, where he joined one of the emerging artistic groups – he performed with Tea-Jazz, a group founded by the Jewish composer Henryk Wars, affiliated with the Lviv Philharmonic. The artist was reunited with his classmate, Albert Harris and Eugeniusz Bodo. He also met his future wife, Renata Bogdańska (who would later marry General Władysław Anders). Whilst on tour, the group found out Germany invaded the Soviet Union. Borucki later joined the band of Feliks 'Ref-Ren' Konarski and continued to perform. As the troupe was waiting for a train, Borucki ran into a Polish sergeant at the platform:
He told us a Polish army was being formed and that he had permission to recruit volunteers. Our pianist, Leszek Krzaklewski, was a lieutenant. He disappeared for several days and came back with a written order for all the members of Ref-Ren's Theatre to come to the post in Totskoye. How happy we were! We headed out almost immediately. It soon turned out other ensembles also decided to enrol in the Polish army.
The conditions the Anders' Army faced on its military route were incredibly difficult – extreme temperatures (spanning from the freezing -45°C to unbearable heat, over 50°C), hunger, typhus, daily burials and dangerous animals. Incredibly enough, the artistic troupes accompanying the soldiers did not lose their spirit and kept on working (different groups were united under the name Polish Parade). Borucki compèred the shows in English and performed – in Iraq, Iran, Palestine, Egypt and the Apennines, on deserts, in the municipal theatres of Tel Aviv and Jerusalem, amongst the sick in hospitals and… for the six-year-old king of Iraq.
Borucki went down in history as the first performer of the iconic war song The Red Poppies on Monte Cassino written by Feliks Konarski and composed by Alfred Schütz. As all accounts stress, the song was written in just one night – from 17 May to 18 May 1944, right before the troops captured the Monte Cassino monastery. However, as Borucki told Anna Mieszkowska in an extended interview, he believed the song ‘emerged in the atmosphere of the many weeks preceding the battle’. Years later, he recounted:
Ref-Ren awoke Ferdek [Alfred Schütz] and me in the middle of the night. I was upset – I had to learn new lyrics at three in the morning… After several sleepless nights, I managed to peacefully fall asleep and they brutally woke me. Irritated, I mumbled this and that: we've been performing for several years now, but no one has ever commanded a rehearsal at such an hour. But right after I read the first words, I knew it was going to be a success.