Sergej Mašera (11 May 1912 - 17 April 1941), naval officer, Lieutenant Commander, national hero and recipient of the partisan commemorative medal, became part of Slovenian and world maritime history owing to his heroic deed, which raised morale among soldiers, became widely known and well thought of at home and abroad, and was considered a great feat of heroism and sacrifice, performed in accordance with international military ethics. On 17 April 1941, after the capitulation of the Yugoslav Army, he blew up, together with Lieutenant Commander Milan Spasić, the destroyer Zagreb in Kotor Bay and lost his life on the ship.
Sergej Mašera was born in Gorica to the family originating from Kobarid. In May 1915, however, the Mašera family left Gorica in the maelstrom of war. After the war and the disintegration of the Austro-Hungarian Empire, the Masheras chose not to return to Gorica owing to the changed political situation as well as Slovenian patriotism and community spirit clearly expressed by Franc, the head of the family, but settled in Ljubljana. Sergej completed his primary as well as secondary education there. After graduating, he enrolled at the Naval Academy in Dubrovnik, where Yugoslav Navy officers were educated since its establishment. After successfully completing his studies in 1932, he began his naval officer career as Sub Lieutenant, initially on the board of the outdated T5 torpedo boat and eventually on the ship Sitnica. As he was attracted particularly to artillery, he decided to specialize in this field. He took the "famous 3rd artillery course" at Kumbor in Kotor Bay, "which gave you more than professors", and completed it in 1934. Thereupon he was transferred to the Artillery Institute at Lepetane, and in 1936 to the Navy Command in Zemun, where he began to prepare for the exam for the senior rank of Lieutenant Commander. During this period, the Yugoslav Navy built three destroyers, named Belgrade, Zagreb and Ljubljana, in Nantes, Glasgow and Split. As a naval artillery specialist, he was selected a member of the commission to test, purchase and contract the Bofors anti-aircraft guns in Sweden, with which these three destroyers were to be armed. In 1938, he indeed travelled to Sweden and worked for a while at the Bofors arms factory. Swedish progressive and, in his opinion, democratic conditions greatly impressed him as well as contributed to his humanistic orientation. The voyage to Sweden also brought him prestige and respect from his comrades.
In March 1941, Mašera was transferred from the destroyer Belgrade to the destroyer Zagreb in Kotor Bay at the time when the war broke out. The ship Zagreb, disguised with olive tree branches, controlled the Bay of Tivat. On April 16, however, the Yugoslav Fleet Headquarters surrendered to the required unconditional capitulation and ordered all crews to hand over their ships, submarines and seacraft to the advancing enemy. As soon as the Yugoslav Army announced its surrender, the destroyer Zagreb’s crew abandoned the ship in great disorder and confusion by order of Captain Nikola Krizomali. Only the two Lieutenant Commanders, artillery specialist Sergej Mašera and torpedo expert Milan Spasić, remained on it. In line with the imparted military doctrine, Mašera did not concede to the capitulation of the Yugoslav Army and Navy. As soon as the crew abandoned the ship, the two officers who remained on its board expertly blew up the ship and sank with it to the bottom of the bay.