HBDJ-21 series
The HBDJ-21 (Menghean: 화전 발사기 대잠수함, Hwajŏn-Balsagi Dae-Jamsuham, "Rocket-launcher, anti-submarine," 21cm caliber) are a family of anti-submarine weapons developed in Menghe for the Menghean Navy. They are usually described as "anti-submarine rocket launchers" or "rocket-propelled depth charge projectors." In their basicASW role, they fire a volley of special 210mm rockets toward a hostile sonar contact. After the rockets strike the surface of the water, they either sink to a pre-set depth and detonate, or home in on the target, depending on the rocket model used. In 2006, the Menghean Navy introduced the H-21ŎD rocket, which allows the system to deploy torpedo decoys.
Wire-guided 533mm torpedoes have maximum ranges far in excess of six kilometers, allowing hostile ships to engage warships armed with HBDJ-21 family launchers with impunity; as such, the system is mainly intended as a last line of defense, to complement longer-ranged weapons such as rocket-deployed torpedoes and ship-launched torpedoes. On board the newest Menghean warships, HBDJ-21 launch systems exclusively use a combination of H-21NS and H-21ŎD ammunition, usually in ratios that favor the latter.
Projectiles
As of 2016, three types of 210mm rocket are available for the HBDJ-21 launcher family. These differ in design but are all compatible with the same launch tubes and share the base designation H-21 (Hwajŏn, 21cm). Two of these are designed to engage submarines, while the third is an anti-torpedo countermeasure intended to jam sonar-guided torpedoes by generating false targets.
H-21DJH
The H-21DJH (대잠수함 / 對潛水艦, Dae-Jamsuham, "Anti-Submarine") is the basic variant of the R-21 which entered service in 1964. It is a direct copy of a similar projectile developed in the Federation of Socialist Republics. The modern version is equipped with an adjustable time fuse, and can be programmed to explode at a pre-set depth based on the detected depth of the submarine; multiple missiles in each salvo may be set at varying depths in case the target dives. The H-21DJH also carries an inertial contact fuse, which will detonate the warhead if it comes into contact with the submarine after already striking the water's surface.
Though designed for anti-submarine operations, the H-21DJH can also be used in the coastal-bombardment role, if programmed to explode on impact. Due to the weapon's short range, low payload, and anti-submarine optimization, this option is not recommended, but can be improvised.
- Weight: 112 kg
- Diameter: 21 cm
- Length: 191 cm
- Warhead: 26 kg high-explosive depth charge
- Range: 300 m to 6000 m
- Depth: 0 m to 500 m
- Sink rate: 9 m/s
H-21NS
The H-21NS (능동 소나 / 能動--, Nŭngdong Sona, "Active Sonar") is a guided H-21 rocket developed in the early 1990s and deployed in 1995. It is fitted with an active sonar seeker in the nose and has control surfaces in the rear, allowing it to maneuver toward a submarine target as it descends. It also has a faster rate of descent than the basic H-21DJH, and carries a shaped charge warhead designed to punch through the hostile submarine's pressure hull on contact. It is also capable of diving to 1,500 meters, a figure in excess of the maximum safe operating depth of all known combat submarines. A 12-round salvo using the H-21NS reportedly has a kill probability of 0.8.
- Weight: 116 kg
- Diameter: 21 cm
- Length: 191 cm
- Warhead: 20 kg shaped-charge warhead
- Range: 600 m to 4000 m
- Depth: 10 m to 1500 m
- Effective homing radius: 200 m
- Sink rate: 18 m/s
H-21ŎD
The H-21ŎD (어뢰 대항책 / 魚雷對抗策, Ŏroe Daehamchaek, "Torpedo Countermeasure") is a softkill active defense countermeasure against enemy sonar-guided torpedoes. Once it comes in contact with the water, the projectile deploys a buoy and wire and remains suspended at a depth of 7 meters. There, it generates extensive sonar noise across frequencies in the wideband acoustic range, overwhelming the torpedo's active and passive sonar system with a large number of regularly regenerated false targets. Unable to distinguish between the countermeasures and the target vessel, and overwhelmed by false signals, the torpedo is lured in circles until it runs out of fuel or power, giving the target vessel time to escape.
A modified version of the H-21ŎD, designated JD-21ŎD, is designed to be carried onboard submarines in side-facing tubes sandwiched between the outer hull and pressure hull. It can be deployed directly into the water, to confuse homing torpedoes fired at the submarine itself or to mask the submarine's location on active and passive sonar.
Notably, the H-21ŎD is only effective against torpedoes which rely on active or passive sonar to find their targets. It is not effective against wake-homing torpedoes.
- Weight: 82 kg
- Diameter: 21 cm
- Length: 190 cm
- Payload: wideband acoustic jammer
- Range: 100-800 m
Launchers
A wide variety of launchers for the H-21 rocket family exist. Launchers designed to handle these rockets all share the base designation HBDJ-21, but they differ in the number of tubes, the type of guidance system used, and the structure of below-deck handling equipment.
HBDJ-21/5
Launcher used on some light patrol craft and submarine hunters starting in 1964, with five tubes in a "W" arrangement. The launcher is fixed in place, usually on the quarterdeck facing forward, and cannot be traversed port or starboard. Instead, it is aimed by steering the ship's bow toward the target. Launchers are elevated and depressed by crew members prior to firing to control range.
HBDJ-21/16
Launcher dating from the same era as the HBDJ-21/5, with two rows of eight tubes each. These launchers can be elevated and traversed by means of hand cranks on either side, but the crew must take cover before firing. Like the 21/5, they have no below-deck systems apart from extra structural supports for the mount.
HBDJ-21/12
The most common HBDJ-21 launcher, this unit uses twelve tubes in a "horseshoe" arrangement. It can be remotely aimed from within the ship and integrated into its combat control system, and is fully stabilized, improving accuracy and response time. It also incorporates a below-deck support system which automatically loads new ammunition into the launcher while it points directly downward and rotates over a single rocket-feeding tube. Total stored ammunition capacity for a single launcher is 60 rounds, though as many as 96 can be carried on expanded systems. This system was first seen on the anti-submarine Kim Chŏl-jin class corvette in 1976.
- Weight: 3,400 kg (empty launcher)
- Tube length: 2 m
- Elevation: -5 to +65 degrees when firing, -90 degrees when reloading
- Traverse: +/-180 degrees when reloading, firing arc limited by ship superstructure
- Traverse rate: 30 degrees per second
HBDJ-21/10
Similar in appearance to the HBDJ-21/16, the HBDJ-21/10 is an entirely different system, and can be remotely aimed and fired from the ship's central control system. It first appeared on the Ri_Sun-hŭi_class_corvettes. Unlike the 21/12 and 21/6, it does not require extensive below-deck support systems, and can be bolted directly onto the deck, as long as it is connected to the ship's power source and its targeting systems. This makes it optimal for small warships, or for retrofitted application to large ones. As a consequence, however, it lacks an automatic reloading system, and must be reloaded by hand.
- Weight: 1,200 kg (empty launcher)
- Elevation: -15 to +55 degrees
- Traverse: +/-90 degrees
- Traverse rate: 30 degrees per second
HBDJ-21/6
A new launcher first seen on the Jŏngdŏk-class frigates and Insŏng-class destroyers. It carries six rocket tubes in a hexagonal arrangement at the center of the mount, which is elevated and depressed by motors on either side. The entire mount is designed with a low radar cross-section so that it does not increase the radar signature of the ship carrying it. As on the HBDJ-21/12, the launcher is automatically reloaded from below decks, but on current Menghean warships it only has a 36-round magazine and the vast majority of the rounds carried are H-21ŎD decoys.
Weight: 2,100 kg (empty launcher)
- Elevation: -15 to +65 degrees when firing, -90 degrees when reloading
- Traverse: +/-180 degrees when reloading, firing arc limited by ship superstructure
- Traverse rate: 90 degrees per second