Subisu CIWS

GBM-23/5/2Y Subisu
3-view diagram of the Subisu CIWS, including a cutaway of the below-deck compartment.
Type	Close-in weapon system
Place of origin	Menghe
Service history
In service	2004–present
Production history
Designed	1998-2004
Produced	2002-present
Specifications
Height	4.18 m (above deck)
Crew	2 (can be automated)
Shell	23×133mm
Caliber	23mm
Barrels	2 × 5
Elevation	-20 to +90 degrees at 60 degrees/sec
Traverse	+135 to -135 degrees
Rate of fire	9,200 rounds per minute (total)
Muzzle velocity	1,109 m/s
Effective firing range	4000 m (aircraft) 3000 m (missiles)
Feed system	linkless feed (16,800 rounds)
Main armament	2 × GP-23/5 rotary cannon 8 × YDG-61 missile

The Subisu (수비수 / 守備手, "defender") is a type of close-in weapon system developed for the Menghean Navy in the early 2000s. Its full designation is GBM-23/5/2Y, but "Subisu" is the more commonly used term.

The armament of the Subisu CIWS consists of two 5-barreled 23mm rotary cannons with a combined rate of fire of 9,200 rounds per minute. This is the same gun used by the GBM-23/5 Bulkkot and the Songrim SR-8 fighter. In addition, the Subisu CIWS carries eight YDG-61 infrared-homing surface-to-air missiles in ready containers, with an additional 24 missiles stored in a below-deck magazine. The addition of missiles gives the Subisu system a longer maximum range and greater redundancy than gun-only CIWS mounts, while requiring less above-deck space than separate gun and missile mounts. In addition to aircraft, helicopters, and missiles, the Subisu system can also engage surface targets and targets on shore.

Development

The Subisu CIWS system branched off of the Bulkkot CIWS during the latter's development. Because the GP-23/5 autocannon had a lower rate of fire than the GP-30/6 used by the GBM-30/6 while firing a smaller round, some designers felt that a twin-gun mount would be preferable to a single-gun one. Additionally, while the GBM-30/6 was usually mounted in pairs, the new close-in weapon system would use single mounts.

Both 10-barrel and 12-barrel versions of the mount were considered early on in development, and found to offer greater weight savings and reliability than a double mount. Nevertheless, the production version was completed with two 5-barrel rotary cannons, as the GP-23/5 was already in mass production with a proven record of reliability and the designers did not have time to develop a new weapon.

Another consideration influencing the Subisu's design was the perceived inadequacy of the YDG-36 ship-based surface-to-air missile. This weapon had very poor accuracy and reliability when first deployed, and even after upgrades in the mid-1990s it still fell short of the Navy's requirements. The desire to replace the YDG-36 dual-quad mount influenced one important requirement in the Subisu CIWS's development: that it be able to fit into the below-deck missile magazine used by the YDG-36 launcher, allowing easy installation on ships built for the old system.

A single Subisu CIWS mount was installed on the Mugunghwa-class corvette Juksun in 2002, taking the place of Juksun's experimental YDG-36 launcher. Trials with the new weapon took place in 2003. The first operational surface ship to receive it was the Chŏndong-class destroyer Pungrang, which was rebuilt with Subisu systems in the forward and aft positions in 2004. Her sister ship Bŏmram was refitted in the same year.

Design

Sensors

The fire-control system on the Subisu CIWS is identical to that used by the GBM-23/5, and consists of an independently elevating and traversing mast with a fire-control radar, a visual-spectrum TV camera, a dual-band infrared camera, and a laser rangefinder. As on Bulkkot, this multi-sensor approach gives it good redundancy against jamming and inclement weather, and allows it to engage surface targets via electro-optical fire control.

The baseline version of the Subisu CIWS lacks its own search radar, and relies on other shipboard platforms to detect and assign targets. On the Subisu-R variant (GBM-23/5/2YR), the mount carries a built-in short-range air search radar, but this version is only used for small craft on the export market.

Guns

The central armament of the Subisu CIWS consists of two 23mm rotary cannons, each with 5 barrels. These are modified versions of the Glasic 23mm rotary cannon licensed to Menghe along with the Songrim SR-8. Each cannon has a rate of fire of 4,600 rounds per minute, for a combined rate of fire of 9,200 rounds per minute. Both guns are externally powered with a reduced rate-of-fire option (300 rounds per minute per gun) for conserving ammunition while engaging surface targets.

Unlike the Bulkkot CIWS, Subisu stores its ammunition in four large horizontal drums located deep below the mount. Ammunition capacity is relatively high, at 8,400 rounds per gun. All ammunition carried by the system uses solid steel APDS projectiles with nylon sheaths, for increased muzzle velocity and range.

Missiles

In addition to its guns, the Subisu CIWS carries the YDG-61 surface-to-air missile. The naval "N" variant of this missile uses an infrared homing guidance system with passive radar homing prongs to track the emissions from an anti-ship missile's seeker, and has a reduced-range fuse to more easily engage sea-skimming targets. Both seeker modes require no further input from the launch platform once the missile is launched, allowing the gunner to select a new target once a missile is fired. Missiles can be fired either individually or in groups, and in trials they achieved a hit probability of 95%.

The Subisu mount carries eight YDG-61 missiles in the ready position, with a single four-cell launcher on each side of the turret. The magazine beneath the turret contains 24 additional reload missiles in six four-cell launchers, for a total of 32. To reload, the mount traverses to a 0-degree bearing, elevates the missile arms directly upward, and lowers the empty (or partially empty) boxes into the empty positions in the reload carousels. The carousels then rotate to bring full missile boxes under the mount arms, which lift them into place with a special chain loading system. The reloading cycle is completely automated, and takes 15 seconds when starting at a 0-degree bearing. Because bearing is fixed during the reload process, the Subisu CIWS cannot engage targets with its guns during reloading.

Supporting equipment

In return for its powerful armament, the Subisu CIWS requires a large amount of below-deck supporting equipment. Its below-deck compartment is 6.7 meters long, 5.7 meters wide, and 4.8 meters deep, corresponding to two decks of a ship. These are the same dimensions as the missile magazine of the YDG-36 naval mount, allowing the Subisu CIWS to be installed as a drop-in replacement in refits.

In a typical crew arrangement, the Subisu CIWS has one operator inside the magazine compartment to monitor the mount's systems and one operator in the combat information center to assign targets and control engagements. As with the GBM-23/5, typical doctrine involves running the gun in a fully-manned manual control state during low-intensity operations, but there is also a fully autonomous state which the crew can activate when the ship is under intense missile attack. In this mode, the Subisu CIWS automatically engages incoming targets in order of threat level, resulting in a faster reaction time.

Variants

GBM-23/5/2YR

A variant with a built-in short-range 3D search radar mounted above the illumination radar. This allows the mount to autonomously track and engage targets, without input from other sensors aboard the ship. This configuration is not used by any Menghean warships, but it has been marketed for export with a focus on small vessels.

Subisu Sohyŏng

The Sohyŏng ("compact") version of the Subisu system carries 16 ready missiles on the mount in two quad-missile boxes per side, similar to the Dungji variant of the GBM-23/5. These missile boxes are not reloadable. The elimination of the missile reload magazine allows a halving in the system's magazine space, so that the Subusu Sohyŏng only takes up one deck of space below the mount. Like the GBM-23/5/2YR variant, this system has been marketed to foreign navies as a weapon for corvettes and light craft, but is not used by the Menghean Navy because the Dungji CIWS achieves similar capabilities without any below-deck footprint.

Users

By ship class

• Menghean aircraft carrier Haebang (after refits)
• Chŏndong-class destroyer (after refits)

By country

• Menghe

See also

• GBM-23/5
• Testudo CIWS