Velebit (pennant number P-01) was a modified Una-class midget submarine and the only submarine to see service with the Croatian Navy. It was built for the Yugoslav Navy during the 1980s where it was named Soča. At the outbreak of the Croatian War of Independence Soča was being overhauled in the Brodogradilište specijalnih objekata division of Brodosplit shipyard in Split, Croatia. Although stripped of all equipment, it was preserved from the retreating Yugoslav forces by the shipyard workers.
With modifications that were aimed at improving the ships endurance by including a diesel generator, it was launched as Velebit (P-01) in 1996. Since 2001, due to battery set malfunction, Velebit was no longer able to submerge, and was constrained to surface operations. After it was decommissioned in 2006, there were unsuccessful attempts of selling it to a foreign buyer. The submarine was then offered to various museums in Croatia, with a final destination still pending.
Design and construction
Velebit was completed as Soča in 1987 at the Brodogradilište specijalnih objekata division of Brodosplit shipyard in Split, Croatia, as the fourth boat in its class. It measures in length, has a draft of , a beam and displaces when surfaced or when submerged. It was constructed as a single hull design with the internal compartment divided into three sections: forward (command/steering) position, exit chamber and the propulsion section in the back. During underwater operations two battery groups with a total of 256 cells power two 20 kW Končar electric motors mounted on a single shaft that spins a five blade propeller. Surface propulsion and battery recharging is provided by a single diesel generator.
Maximum speed is underwater and surfaced. The boat's range is with a speed of . It has an underwater endurance of up to 6–7 days which is an improvement compared to 96 hours of other Una-class boats. Maximum diving depth is .
Because the class was designed with reconnaissance, small scale minelaying and special operations in mind, it does not possess any offensive weapons such as torpedoes. The submarine was to use its small dimensions to easily maneuver in the relatively shallow waters of the Adriatic Sea, staying undetected and transporting up to six special forces personnel who had 6–12 limpet mines and four AIM-M70 (M70/1) bottom mines or four R-1 submersibles at their disposal. Velebit had a crew of four.
Service
Before the Croatian War of Independence Velebit served with the 88th Submarine Flotilla of the Yugoslav Navy entering service during the late 1980s. Velebit, then named Soča, was like other Una-class submarines, named after rivers in Yugoslavia. In 1991, it was being overhauled in Brodogradilište specijalnih objekata until the beginning of the war, when Croatian forces captured it. In 1993, Brodarski Institut (BI) of Zagreb started a modification program to improve the operational capabilities of the submarine captured two years earlier. The hull was lengthened by to create space needed for the installation of a single MTU 105 kW diesel generator, a feature the original Una-class design lacked. A new steering system developed by BI was also installed.
It was recommissioned as Velebit in 1996. According to the 2007 edition of The Naval Institute Guide to Combat Fleets of the World, Velebit was fitted with a STN-Atlas Elektronik PP-10 active and PSU-1-2 passive sonar and a portable navigational radar may have been used on board along with the GPS. The claim is contradicted by other sources with news reports stating the submarine was completed without an active sonar, effectively being "blind" underwater. During the 1990s Velebit had the pennant number "3" painted on its side. Since 2001, after the existing battery set needed for underwater propulsion expired and needed replacement, crew training and boat operations were limited to surface drives.
Decommissioning and aftermath
In February 2005 Velebit was raised from the sea, placed on a small platform within the Lora Naval Base and has remained there since. In June 2006 the Croatian Ministry of Defence released the Croatian Armed Forces Long Term Development Plan 2006–2015 () in which it was stated that: