Taiwan Strait and South China Sea offshore islands. Since the 1990s the Navy has grown in importance as the emphasis of the ROC's military doctrine moves towards countering a possible People's Republic of China (PRC) blockade, as well as offshore engagement. As of 2004 the ROCN had been working hard to expand its capability in electronic and anti-submarine warfare, as well as the replacement of antiquated warships and support vessels. While for many years the ROCN operated hand me down and foreign designed vessels in recent years they have been operating a higher number of indigenous platforms, sensors, and weapons much of it made by the National Chung-Shan Institute of Science and Technology. In 2018 Lungteh Shipbuilding was awarded a contract to produce eleven Tuo Chiang Block II corvettes and four minelayers for the Taiwanese Navy. In April 2020 in response to the COVID-19 pandemic the ROCN cut short their semi-annual goodwill mission to Central and South America. The flotilla consisting of two frigates and a supply vessel was subject to 30 days of quarantine after returning to Taiwan. In April 2020 Taiwanese boatbuilder Karmin International Co., Ltd. won a NT$450-million (US$14.9-million) contract to supply the Republic of China Navy with eighteen special operations watercraft and eight RIB tenders, the later for the Cheng Kung-class frigates. Delivery is scheduled for June 2022. The contract covered only the watercraft themselves with their machine guns, infrared equipment, and boarding ladders sourced separately. Rank and rating insignia Officer ranks Other ranks Equipment Traditionally, most ROCN equipment has been purchased from the United States. The ships themselves have often been older, second-hand vessels without the newest technology. More recently, however, several ships have been built domestically under licence or through domestic development. The ROCN has also purchased s from France and s from the Netherlands as well as four U.S. (renamed Keelung) destroyers originally intended for Iran. Despite the ROCN refurbishing and extending the service life of its vessels and equipment, it has suffered from procurement difficulties due to pressures exerted by the PRC. It has only two useful submarines. The U.S. has approved sales of eight new diesel-powered submarines but lacks the manufacturing capability to make the engines; at the same time, threats from the PRC prevent the necessary technology transfer from other countries. Furthermore, the Legislative Yuan did not approve the budget and thereby slowed the opportunity to procure the badly needed