All in all, air defence — or the lack of one — was a very restrictive factor in the tactical usefulness of the Parchim design. Anti-submarine warfare A major evolution over the old HAI III design was the new hydro-acoustic system. The sonar suite consisted of a bow sonar and a variable depth dipping sonar. The sonar screen was panoramic, meaning that it gave a two dimensional radarscope-like view of the surrounding waters. This was a major improvement over the old auditive system in the HAI III class. Another weakness of the old HAI III was its inability to 'see through' water layers with different temperatures. While sound propagates pretty well in water of the same temperature, it gets easily disturbed by even modest differences in water temperature. Especially in the hot summer months these natural occurring phenomena give submarines an easy hide out for probable sub-chasing surface vessels. A solution is the use of a 'dipping sonar', which in a way is nothing more than a small sonar attached to a long cable. By using this device the Parchim's sonar system was able to search the different water layers. The Parchims were also provided with capable anti-submarine warfare weapons. The torpedo tubes were loaded with acoustical and/or wire guided torpedoes. This gave the Parchims a precision submarine strike capability. The two RBU-6000 depth charge rocket launchers created a barrier defense against submarines, incoming torpedoes and frogmen. Though relatively unsophisticated by western standards, the RBU-6000 was a very successful and popular system, used on many small or large surface ships. It consisted of a twelve launch tubes for unguided rockets, armed with a compact but powerful depth charge. Rockets were directed by simply changing the angle of the tubes and thereby the ballistics of the unguided rockets. The launcher could elevate between -15° and +60°, and could traverse 180°, with each launcher thus covering one side of the ship. Range was between 350 m and 6000 m, and the charges could reach 500 m deep. The rockets, RGB-60's, weighed of which was a high-explosive warhead. The ammunition was swiftly and automatically reloaded from a magazine below deck, by turning the tubes 90° vertically. Maximum magazine capacity was 96 rounds. The whole system was remotely directed by the Burya fire control system. The RBU-6000 could also be used for shore bombardment. The Parchims were also able to simply drop bigger and