The Hrabri-class were the first submarines to serve in the Royal Yugoslav Navy (KM),[a] and after extensive sea trials and testing Hrabri sailed from the UK to the Adriatic coast of Yugoslavia, arriving in April 1928.

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.

The naval policy of the Kingdom of Serbs, Croats and Slovenes (the Kingdom of Yugoslavia from 1929) lacked direction until the mid-1920s,[1] 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.

[4] 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.

[5] Like her sister submarine Nebojsa, Hrabri was of a single hull design with a straight stem, circular cross section and narrow pointed stern.

[13] For surface running, Hrabri was powered by two Vickers V12 diesel engines designed in 1912 that were rated at a combined 2,400 brake horsepower (1,800 kW) at 380 rpm.

The naval historian Zvonimir Freivogel states that on a 15-day Mediterranean cruise, Nebojša needed 420 kg (930 lb) of replacement screws.

Until the destroyer leader Dubrovnik was commissioned in 1932, the Hrabri-class boats had the heaviest armament of any Royal Yugoslav Navy vessel.

When trial diving on another occasion, Hrabri listed sharply to starboard and the bulwark around the bridge was damaged by waves.

The trial and training phase was extensive, and once it was completed, Hrabri and Nebojša sailed to Portland where they took onboard their complement of torpedoes, before returning to Newcastle.

[19] En route one of the submarines suffered from engine trouble and the group had a five-day stopover at Gibraltar for repairs.

They then had a five-day visit to Algiers in French Algeria and a brief stop at Malta before arriving at Tivat in the Bay of Kotor on the southern Adriatic coast on 5 April.

On 16 August a serious accident was averted aboard Hrabri in the narrow harbour entrance at Šibenik in central Dalmatia.

[20] In May and June 1929, Hrabri, Nebojša, Hvar and six 250t class torpedo boats accompanied the light cruiser Dalmacija on a cruise to Malta, the Greek island of Corfu in the Ionian Sea, and Bizerte in the French protectorate of Tunisia.

[20] In 1932, the British naval attaché reported that Yugoslav ships engaged in few exercises, manoeuvres or gunnery training due to reduced budgets.

[23] In 1933, the attaché reported that the naval policy of Yugoslavia was strictly defensive, aimed at protecting her more than 600 km (370 mi) of coastline.

[24] On 4 October 1934, Hrabri and the Osvetnik-class boat Smeli commenced a training cruise in the Mediterranean involving sailing around Sicily independently and meeting at Bizerte.

[25] In 1937, Hrabri participated in a cruise through the eastern Mediterranean along with Smeli, the flotilla leader Dubrovnik and the seaplane tender Zmaj.

The outbreak of World War II less than a year later meant that the ordered boats were never delivered and the Hrabri class had to continue in service.

The Yugoslav military largely reflected this division, few considering interwar Yugoslavia worth fighting or dying for.

[27] When the German-led Axis invasion of Yugoslavia commenced on 6 April 1941, the entire submarine flotilla was docked in the Bay of Kotor.

[3][14][26] In April 2013, the 85th anniversary of Hrabri's arrival at the Bay of Kotor was marked by an event in Tivat, attended by dozens of former Yugoslav submariners.