The Type 037 corvette is a series 400–500 ton corvette type classes in service with the People's Liberation Army Navy. Unlike western navies, the People's Liberation Army Navy does not have dedicated patrol boats in its inventory. Instead, a large variety of corvette type classes, in the form of missile boats and submarine chasers fulfill the tasks of patrolling China's territorial waters. The Egyptian Navy operates eight vessels. Type 037 Hainan-class submarine chaser The Type 037 submarine chaser (NATO reporting name: Hainan class), is a class of submarine chaser of the People's Liberation Army Navy. It was designed by China to replace the Soviet S.O.-1 class submarine chaser. In addition to anti-submarine warfare missions, these simple yet effective units are also capable of a wide variety of missions such as mine laying and patrol. These boats were first equipped with Soviet Tamir-11 (MG-11, NATO reporting name: Stag Hoof) hull-mounted sonars which had a typical range of , but in the 1970s, they were superseded by domestic Chinese SJD-3 sonar, which is modification of original MG-11: instead of being fixed to the hull, SJD-3 has a telescoping arm, so when not in use, the sonar is stored in the hull, and when deployed, the sonar is lowered into water several meter below the hull, thus increased detection range by avoiding baffles generated by the hull. During the Sino-South Vietnamese naval clashes on 19 January 1974, two boats of this class, # 281 & # 282 (two out of the eight total in Chinese inventory) participated in the latter half of the battle, the fastest Chinese units in the conflict. Originally the units were waiting at Yongxing Island, but due to the problem of communications, they were not notified until the battle was already in progress. Over 100 were built, but as newer submarine chasers enter service, this class is steadily being decommissioned. A number of these ships have subsequently been exported to Bangladesh, Egypt, North Korea, Pakistan and Myanmar. On October 13, 2013, a North Korean Type 037 was lost off Wonsan with the loss of at least nineteen of her crew. She may have been in collision with another Korean People's Navy ship. It is understood that four Type 037 submarine chasers were modified and became known as the Type 037 Mod (NATO: Haijiu class). In PLAN service, pennant numbers as follows: 601－610, 622, 625－629, 639, 650, 673, 674, 677,