During the April War, Spasić, along with his fellow Lieutenant Sergej Mašera, scuttled the destroyer Zagreb in the Bay of Kotor near Tivat to prevent it from falling into the hands of the Italian Royal Navy.

He later enrolled in the Naval Military Academy (VII class) in Dubrovnik alongside Sergej Mašera, who would later turn out to be a future comrade.

At the time of outbreak of the April War in 1941, Spasić was a lieutenant on the destroyer Zagreb stationed in Dobrota (Bay of Kotor).

Zagreb and the destroyers Beograd and Dubrovnik were the most recent Royal Yugoslav Navy ships at that time.

The crews of the ships stationed in the Bay of Kotor were instructed not to open fire on the Axis forces and to surrender peacefully.

There was little discussion of Spasić and Mašera until the 1960s, following the democratization of the Yugoslavia (Economic reform 1964 /1965) The French produced a film Flammes sur l'Adriatique (Flames on Adriatic, also known as Adriatic Sea of Fire)[2][3] in 1968, dedicated to this event and directed by Alexandre Astruc and Stjepan Čikeš.

Spasić and Mašera were posthumously awarded the Order of the People's Hero of Yugoslavia by decree of President Tito on 10 September 1973, the 30th anniversary of the establishment of the Yugoslav Navy.