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. While the HBDJ-21 family originated with licensed copies of the Letnian RBU-6000 and RBU-2500 launchers, over time Menghe developed domestic tube arrangements with no Letnian counterpart, as well as new ammunition types. Therefore, it is today considered a different weapon family.
These weapons are usually described as "anti-submarine rocket launchers" or "rocket-propelled depth charge projectors." In their basic ASW role, they fire a volley of special 210mm rockets toward a hostile sonar contact. After the rockets strike the surface of the water, they sink to a pre-set depth and detonate. Today, lightweight torpedoes like the YŎ-35/2 torpedo have largely supplanted the HBDJ-21 in its anti-submarine role, but the family of mounts are still used to deploy torpedo decoys and hardkill anti-torpedo countermeasures.
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, the third is a softkill anti-torpedo countermeasure intended to jam sonar-guided torpedoes by generating false targets, and the fourth is a hardkill anti-torpedo countermeasure which detonates at a shallow depth in the path of an oncoming torpedo.
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 Letnia. 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 1998. 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-21ŎDG
The H-21ŎDG (어뢰 대항책 기윽 / 魚雷對抗策기윽, Ŏroe Daehamchaek Giŭk, "Torpedo Countermeasure G") is a softkill 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.
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
H-21ŎDN
The H-21ŎDN (어뢰 대항책 니은 / 魚雷對抗策니은, Ŏroe Daehamchaek Niŭn, "Torpedo Countermeasure N" is a hardkill countermeasure to defeat enemy torpedoes of all types. Like the H-21DJH, it sinks to a pre-set depth after striking the surface and then detonates. The main difference is that unlike the H-21DJH, it is fired ahead of the sonar contact generated by an incoming torpedo, in the hope that one charge detonates close enough to the passing torpedo to detonate its warhead or damage its seeker or motor. Because of the larger warhead and the importance of reducing lag and dispersion, it has a shorter range of 1500 meters. In trials, the H-21ŎDN reportedly achieved a kill probability of 70% against training torpedoes when fired in a 12-round salvo. Practical kill probability depends on the accuracy with which the torpedo is being tracked and whether the torpedo is following a straight or curving course.
- Weight: 124 kg
- Diameter: 21 cm
- Length: 190 cm
- Warhead: 41 kg high-explopive charge
- Range: 300 m to 1500m
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. Belived to be a licensed copy of the RBU-2500. 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, and are reloaded by hand.
HBDJ-21/12
The most common HBDJ-21 launcher, this unit is a licensed copy of the RBU-6000. It has twelve tubes in a "horseshoe" arrangement, and can be remotely aimed from within the ship using a computer station in the combat information center. It also integrates a below-deck ammunition hoist which rams rockets into the vertically elevated launcher - though crew members several decks below in the magazine must still load rockets onto the bottom of the hoist. Total stored ammunition capacity for a single launcher ranges from 60 to 96 rounds.
- 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-21/6
This launcher was first seen in 2008 on the new corvette Mirun. It consists of six 210mm tubes in a 2x3 lengthwise grid, half the number on the common HBDJ-21/12. This launcher type cannot be reloaded automatically; instead, crew members must manually insert rockets into the tubes from the rear. Unlike the HBDJ-21/5, however, the launcher can traverse and elevate mechanically based on information from the ship's control room. By the time this launcher was introduced, the HBDJ-21 was obsolete as an anti-submarine weapon, having been fully supplanted by Menghean torpedoes and rocket-deployed torpedoes. It is apparently used exclusively for deploying countermeasures as a defense against acoustic homing torpedoes, and on all of the ships that carry it, the mount faces aft.