The Type 037-I (NATO codename: Haijiu class) anti-submarine craft is a lengthened version of the Type 037 (Hainan class) with upgraded armaments and sensors. As the Type 037 cannot fulfil the PLA Navy’s requirement to operate in the South China Sea, an improved variant was proposed in 1974. However, the development of the vessel did not start until 1978. Construction of the first boat 688 began in 1981 and the vessel was handed over to the PLA Navy in 1984. Only four vessels (688, 693, 694, and 697) have ever been built, suggesting that the design may not be fully successful.
The Type 037-I is generally similar to the Type 037 in appearance, but with its hull stretched by 4m. The displacement was therefore increased by 45t, providing an extra 30t storage capacity for fuel/water.
The Type 037-I can be distinguished by its bulky radome positioned on the bridge roof ahead of the tripod mast. The radome accommodates a long-range air/surface search radar (NATO codename: Round Ball) for air surveillance and early warning roles. A Thomson-Sintra SS 12 variable-depth sonar (VDS) is fitted to boat 688 and 693 in place of the aft twin 57mm AAA gun mount.
Type 037I Haijiu class ASW patrol craft (Chinese Internet)
The vessel has two manually operated Type 66 dual-barrel 57mm/70-calibre AAA guns (one front, one rear, hull 697 has its rear 57mm gun removed). The AAA gun fires 6.31kg shells at 120 rounds/min to a maximum range of 12km for airborne targets. There are also two Type 69 dual-30mm automatic AAA guns, firing shells at a rate of 360~400 rounds/min to a range of 4km for airborne targets.
The vessel has four Type 87 (Chinese copy of the Russian RBU-1200) 240mm five-tubed antisubmarine rocket launchers installed on the bow deck, which deliver 34kg warhead to a range of 1,200m. There are also two BMB-2 depth charge mortars, two depth charge racks, and two mine rails fitted on the stern deck.
The vessel has one 'Pot Head' navigation/surface search radar and one 'Round Ball' fire control radar.
The propulsion system consists of four diesels rated at 8,800hp. The boat has two shafts which give a maximum speed of 28 knots. Some boats were later refitted with four 12VE230ZC-II diesel rated at 10,000hp, increasing the maximum speed to 30 knots.
