The Orjen class were motor torpedo boats (MTBs) built for the Royal Navy of Yugoslavia in 1936 and 1937. A total of eight boats were built by the Lürssen Shipyard at Vegesack, Germany. They were based on the German S-2 MTBs, and their primary armament was torpedoes launched from two torpedo tubes, with anti-aircraft protection provided by a gun and a machine gun. At the start of the April 1941 Axis invasion of Yugoslavia, two boats managed to escape to Alexandria in Egypt where they served under the operational command of the British Mediterranean Fleet and under the administrative control of the Yugoslav government-in-exile. Their duties included convoy escort duties and operations against Vichy French forces in Syria. The remaining six boats were captured by Italian forces and commissioned in the Regia Marina (Royal Italian Navy) with modified anti-aircraft armament, and were heavily employed in the Aegean Sea. They were also used by the Italians as the model for the Italian-built CRDA 60 t motor torpedo boats and the submarine chasers of the VAS class.
At the time of the Italian armistice in September 1943, one boat was scuttled by its crew. Another was damaged by its crew, but captured and repaired by the Germans and transferred to the National Republican Navy of the Italian Social Republic for use as a harbour defence vessel at Venice. This boat was later reclaimed by the Germans, and was mined then sank in a storm off the Italian coast in September 1944. The four other boats were taken over by German forces and commissioned in the Kriegsmarine (German Navy), but most suffered from engine problems. They served as part of the 24th S-Boat Flotilla, largely in the Aegean Sea, until they were finally stricken at Salonika in September 1944 as the Germans withdrew from Greece. The two boats that had escaped to the Allies in 1941 returned to Yugoslavia after the war. They were commissioned in the new Yugoslav Navy and remained in service until the early 1960s.
Background Following its creation in 1921, the Royal Navy (; KM; Краљевска Морнарица) of the Kingdom of Serbs, Croats and Slovenes (from 1929, the Royal Navy of Yugoslavia) was determined not to repeat the mistake of its predecessor, the Austro-Hungarian Navy, with its late adoption of motor torpedo boats (MTBs). Thus, in 1926, the KM had ordered two MTBs based on John I. Thornycroft & Company's existing class of Coastal Motor Boats from the United Kingdom. These boats entered KM service as the in 1927. Plans to order more were derailed by a combination of negative assessments during their sea trials and crew training, combined with the advent of the Great Depression in 1929. During the early 1930s, Yugoslavia faced an economic recession which was further complicated by internal political instability. In the mid-1930s, the Yugoslav government sought to improve relations with Italy and Germany to create new economic opportunities for the country. Such cooperation resulted in the acquisition of new German-constructed ships for the KM, which had previously obtained ships from France and Great Britain. In 1936 the KM ordered eight MTBs () that were to be built by the Lürssen shipyard in Vegesack, Germany, based on the existing German design of the S–2 class.
Description and construction The Orjen-class boats were an improved version of the S–2 class, designed with round-bilged displacement hulls which combined a high degree of seaworthiness with strength and light weight thanks to their composite construction using wood and steel. The double hull was constructed of mahogany arranged diagonally over steel frames, unlike the light alloy used in the original S-2 boats. The engines were also mounted on steel bearers. They had a flush deck without a raised forecastle, an enclosed steering room below an open command bridge. A searchlight and small antenna mast were also attached the roof of the steering room. The antenna stretched from this mast to the aft antenna mast near the aft gun mount. A lookout platform with a tall signal mast was located aft of the bridge. Above the engine rooms was a low superstructure with engine skylights, and aft of this was a low deckhouse above the crew accommodation, which also supported the aft gun mount.
The boats were larger and heavier than the original S-2 class, measuring at the waterline and in length overall, with a beam and a draught of . Their design displacement was and fully loaded they displaced . The boats were powered by three Daimler-Benz BF2 12-cylinder four-stroke petrol engines with compressors. Each engine was coupled to a shaft with a single propeller, the forward-mounted engine drove the central shaft and the outer engines drove the port and starboard shafts. The main rudder was semi-balanced, and there were also two small additional rudders to achieve the Lürssen effecta reduction in wave-making resistance that forces the water under the hull outward, lifting the stern and reducing drag. Together, the three engines were rated at between , giving the boats a maximum speed of . At full load displacement generating without using the compressors, the boats could achieve a top speed of only , but with the compressors and the Lürssen effect, the maximum speed could be achieved. A six-cylinder Maybach S5 auxiliary cruising engine rated at was coupled to the central shaft with a chain, and powered the boats to a maximum speed of . The boats carried of gasoline, which gave them a range of at , at and at 7 kn. The Orjen-class boats had a crew of four officers, eleven petty officers and four sailors, but there was not sufficient accommodation on the boats for the whole crew. The officers and higher-rated petty officers had their accommodation aft of the engine rooms and on either side of the aft magazine, and the lower-rated petty officers and sailors had their accommodation located forward on either side of the forward magazine.
The primary armament of the boats consisted of two torpedo tubes, which were mounted forward in the open, unlike later German S-boats that had their torpedo tubes enclosed. The boats could carry four torpedoes, with one loaded in each tube and a reload secured aft of each tube. The boats carried the French torpedo, which was launched by a combination of compressed air and an explosive charge. For anti-aircraft defence a single Bofors gun was mounted on the aft deckhouse, for which 200 rounds were carried aboard. This gun supplemented by a single Zbrojovka Brno (ZB) Model 60 machine gun mounted forward between the torpedo tubes. Two depth charge racks were also installed.
The boats were built in 1936 and 1937, with the eighth boat delivered in late 1937. Included in the contract were three replacement engines, two spare auxiliary engines and spare parts. In the late 1930s the Francophile faction of the KM proposed that all KM warships be re-equipped with French 21 in torpedoes, and the torpedo officer responsible for the Orjen class was sent to Saint-Tropez in France in 1937–1938 to supervise production of forty torpedoes for the KM. Delays meant that by 31 July 1938 only five had been delivered, meaning that most of the Orjen-class boats were not fully armed more than a year after they had been delivered. Diplomatic pressure resulted in faster production, but the last torpedoes were only delivered immediately prior to the outbreak of World War II on 1 September 1939. In 1938, four more boats were ordered, probably to be powered by MB 500 diesel engines rather than the petrol engines fitted to the first eight boats, for a sum of 3.7 million Reichsmarks, but the contract was cancelled due to the outbreak of war.
Boats The boats were named after Yugoslav mountains, and had their tactical numbers stencilled on their bows. Name Tactical No. Namesake Builder Laid down Launched Completed First Italian designation(1941) Second Italian designation(1942) German designation(September 1943) First Yugoslav designation Second Yugoslav designationOrjenOrjenLürssen, Vegesack, Nazi Germany Velebit Velebit Dinara Dinara Triglav Triglav Suvobor Suvobor Rudnik Rudnik Kajmakčalan Kajmakčalan Durmitor Durmitor Sources: , , ,
Service history
Royal Yugoslav Navy service Prior to the outbreak of war, and during the war until the April 1941 Axis invasion of Yugoslavia, all eight Orjen-class boats served with the 2nd Torpedo Division. When the invasion began on 6 April, Velebitas division leader with the divisional commanding officer Niko Kosović aboard, Kajmakčalan, Durmitor, Dinara, Triglav and Suvobor were deployed at Šibenik on the central Dalmatian coast, along with the two Uskok-class MTBsalso allocated to the 2nd Torpedo Division, and four s of the 3rd Torpedo Division. At the time, Orjen was being refitted at the Naval Arsenal at Tivat in the Bay of Kotor, and Rudnik had also been sent to the Bay of Kotor, possibly as an escort for the tanker Perun.
On 8 April, the combined 2nd and 3rd Torpedo Divisions were tasked to support an attack on the Italian enclave of Zara (Zadar) on the Dalmatia coast, which the Yugoslav High Command feared would be used as a bridgehead during the invasion. They were subjected to three Italian air attacks and, after the last one, sailed from the area of Zaton into Lake Prokljan, where they remained until 11 April. On 10 April, the establishment of an Axis puppet state carved out of Yugoslaviathe Independent State of Croatiawas announced, and the attack on Zara was cancelled. The divisional commander of the 3rd Torpedo Division, Ivan Kern, found that the crews of his division were refusing to follow orders, so he left his command and led the boats of the 2nd Torpedo Division to the Bay of Kotor, where they arrived on 13 April. The following day the crews became aware that a general Yugoslav surrender was imminent, and they were ordered not to provoke the invading forces. On 16 April, the evaded the Italians and escaped from the Bay of Kotor. Some officers and crew of the 2nd Torpedo Division also wished to evade capture by the Axis and continue their fight alongside Allied forces., but the crews of Suvobor, Velebit and Rudnik were opposed. By 17 April, the complete collapse of Yugoslav defences and the general surrender were imminent, prompting Kern to lead Durmitor, Kajmakčalan, Triglav and Dinara out of the Bay of Kotor that day. A fire in Triglavs engine roomsabotaged by one of her officerscaused her to turn back, and Dinara sailed to her assistance. Upon docking, both crews deserted. These two boats were later seized by the Italians, along with Suvobor, Velebit, Rudnik and Orjen.