Complex sentence: Spasić and Mašera were declared People's Heroes of Yugoslavia by decree of President Tito on 10 September 1973, the 30th anniversary of the Yugoslav War Navy.
Split into simpler sentences: Spasić and Mašera were declared People's Heroes of Yugoslavia by decree of President Tito. This was done on 10 September 1973, the 30th anniversary of the Yugoslav War Navy.