dredging operations in the area of responsibility that includes the training requirements for the Pakistan Navy's personnel at the deeper ocean which is conducted by a dedicated Sail Training Vessel. The 21st Auxiliary Squadron consists of , a tall ship acquired from the United Kingdom in 2010, PNS Behr Khusha, a dredging vessel commissioned from China in 2008, and , that was commissioned from Japan in 1983. Aircraft The Aircraft in the Pakistan Navy provides the logistical support to the navy's readiness at all level of commands and serves as the supply platform, through helicopters, to conduct the search and rescue, special operations, anti-submarine warfare (ASW), and the anti-surface warfare (ASuW). Unlike the Indian Navy, the Pakistan Navy does not have the rapid aircraft carrier based strike capability but relies its aerial strike operations from clear and traditionally long landing platform built at the Mehran Naval Air Station in Karachi. After realising the failure to protect the harbour from the attacks of the Indian Navy in 1971, the Navy took the research on using the aircraft on sea in an attempt to lessen the dependence on the Pakistan Air Force, which already covers the airspace of Pakistan, and established the naval aviation branch, the Naval Air Arm, in 1974. The Navy's principal aerial fighting branch is known as the Naval Air Arm whose initial pilots' training took place at the Air Force Academy in Risalpur. The Navy operates the Fokker F27 Friendship, Breguet Atlantique, Lockheed P-3 Orion, ATR 72, and Hawker 800 as their fixed-wing aircraft inventory. The rotary-wing aircraft in the naval air arm includes the Harbin Z-9 and the Westland Sea King while the Lynx helicopters have now been removed from active service due to maintenance issues, and a tender has been issued for their removal. In addition, there are numbers of aircraft active in the Maritime Security Agency (MSA). Weapon system and air defence Current weapon systems in the Pakistan Navy is entirely composed and focused towards missiles, serving as both weapons or a defence from a threat. In 1971 with the Indian Navy's introduction of anti-ship missiles, Navy had the strong emphasis on classically using the artillery and ammunition focusing towards the vintage tactics witnessed in the previous naval wars fought in the World War II. The Navy's primary air defence included the usage of the LY-80, FM-90, FIM-92 Stinger, RBS 70, Feinu-6, Anza and the