Hrabri (Brave) was the lead boat of the Hrabri-class submarines; built for the Kingdom of Serbs, Croats and Slovenes– Yugoslavia by the Vickers-Armstrong Naval Yard in the United Kingdom. Launched in 1927, her design was based on the British L-class submarine of World War I, and was built using parts from an L-class submarine that was never completed. The Hrabri-class were the first submarines to serve in the Royal Yugoslav Navy (KM), and after extensive sea trials and testing Hrabri sailed from the UK to the Adriatic coast of Yugoslavia, arriving in April 1928. The submarine was armed with six bow-mounted torpedo tubes, two deck guns, one QF 2-pounder () L/39 anti-aircraft gun and two machine guns. Its maximum diving depth was restricted to by Yugoslav naval regulations.
Prior to World War II, Hrabri participated in cruises to Mediterranean ports. In 1933–1934 she was refitted, her superstructure was extensively modified and the 2-pounder gun was replaced with a single Hotchkiss M1929 anti-aircraft machine gun. By 1938 the class was considered to be obsolete, but efforts to replace them with modern German coastal submarines were stymied by the advent of World War II, and Hrabri remained in service. Immediately before the April 1941 German-led Axis invasion of Yugoslavia, Hrabri conducted patrols in the Adriatic Sea, and was then captured by Italian forces. She was given the number N3, but after an inspection she was scrapped.
Background
The naval policy of the Kingdom of Serbs, Croats and Slovenes (the Kingdom of Yugoslavia from 1929) lacked direction until the mid-1920s, although it was generally accepted by the armed forces that the Adriatic coastline was effectively a sea frontier that the naval arm was responsible for securing with the limited resources made available to it. In 1926, a modest ten-year construction program was initiated to build up a force of submarines, coastal torpedo boats, and torpedo and conventional bomber aircraft to perform this role. The Hrabri-class submarines were one of the first new acquisitions aimed at developing a naval force capable of meeting this challenge.
Hrabri (Brave) was built for the Kingdom of Serbs, Croats and Slovenes by the Vickers-Armstrong Naval Yard, on the River Tyne, in the United Kingdom. Her design was based on the British L-class submarine of World War I, and she was built using parts originally assembled for HMS L67, which was not completed due to the end of World War I. The British Royal Navy (RN) cancelled the order for L67 in March 1919, and the partially constructed hull was launched on 16 June to free up the slipways on which it was being built. In November the hull was sold by the RN to the shipyard, and once the contract with the Yugoslavs was signed they were brought back onto the slipways and completed to a modified design. The British boats were chosen for two reasons: a visit to the Kingdom of Serbs, Croats and Slovenes by HMS L53 in 1926, and a British credit for naval purchases which included spending some of the funds in British shipyards.
The L-class boats were an improved version of the and achieved a better relationship between displacement, propulsion, speed and armament than their predecessors, including a powerful armament of both torpedoes and guns. The class was designed for operations in the North Sea in World War I, but due to their considerable range they were deployed around the world during the interwar period by the RN, including in the Mediterranean, and three were still in service at the outbreak of World War II.