but using CSIST produced fire control radars instead. Currently four different variants exist within this class, the original Ching Chiang patrol ship constructed with four HF-1 (one existing in this configuration). On 29 December 2010, two LSTs () and four remaining of Adjutant-class coastal minehunters were retired. In 2011, the navy retired several vessels. On 31 October, all eight PCL in the 124th Fleet were retired. On 28 December, the two Lung Jiang-class (PSMM Mk5) guided missile patrol boats (PGG 601 and PPG 602) of the 131st Fleet were retired from ROC Navy service, after entering service in 1978 and 1981 respectively. In June 2018, two s of the US Navy, ex- and ex-, were handed over to the Government of Taiwan for the Republic of China Navy. The transfer cost was an estimated US$177 million. The transfer of the ships includes the advanced AN/SQR-19 Multi-Function Towed array sonar. Taiwan had previously been blocked from acquiring the AN/SQR-19, and the transfer of the system points to an anti-submarine focus in line with the Knox-class frigates they will likely replace. The keel of a new rescue and salvage ship was laid in March 2022. Indigenous "Landing Platform Dock" / Amphibious Assault Ship In September 2018, Taiwan confirms contract for first amphibious assault ship built in Taiwan. It will be built by CSBC Corporation, a local shipyard. Four are planned with the first to be entering service around 2021. It is roughly similar to US Navy's San Antonio class, but with a slightly smaller displacement. Support features include a full hospital, well deck, full aviation facilities, storage for wheeled vehicles, and dedicated accommodations for a full battalion of Marines. The vessel design will be armed with a 76 mm naval gun in the primary position, a close-in weapon system (CIWS) turret, two 12.7 mm machine gun positions in the forward section, and launchers that can deploy the Hsiung Feng II and III family of anti-ship and land-attack cruise missiles. The primary sensor is expected to be a naval version of the indigenous CS/MPQ-90 Bee Eye AESA radar. Fleet Air Defense Upgrade / Hsun Lien Project The ROC Navy currently lacks a modern fleet defense system. Its destroyers currently use obsolete Mark 26 missile launchers designed from the 1970s and does not currently have a modern centralized air defense combat system like the Aegis. Past US administrations rejected the sale of Aegis radar