Chŏl-u
Chŏl-u (Menghean: 철우 / 鐵雨, "Iron Rain") is a dual-purpose cluster munition developed by Menghe. It is effective against a variety of targets, including armored vehicles, light structures, and infantry in the open. It is designed to be deployed from artillery shells, artillery rockets, and aircraft bombs. Among infantry of the Menghean Army, it is sometimes called Pokjuk ("firecracker") due to the rattling series of explosions released by each bomb or shell.
Strictly speaking, the term Chŏl-u is applied to two separate Menghean submunitions, with the sub-designations 81-nyŏn and 07-nyŏn. These are the units introduced in 1981 and re-introduced with improvements in 2007, respectively (see "service," below). They differ in drag and fusing arrangements but use an identical explosive charge and have the same stacking dimensions. Chŏl-u 07-nyŏn has a much lower failure rate.
Design
Chŏl-u 81-nyŏn
The 81-nyŏn submunition consists of a small cylinder 40 millimeters in diameter with a conical fin assembly on the top side. When stored inside a canister round, Chŏl-u submunitions can be stacked end-on-end, with each unit's tail assembly fitting into another's nose.
The tail assembly consists of four thin metal fins, which are attached by torsion springs to a hollow metal rod. When the rounds are stacked, as above, these are compressed against the munition in the shape of a cone, but when the rounds are scattered the springs force the fins open, creating drag and pointing the submunition's nose downward. Because the fins are curved, they rotate in flight, unscrewing the fuse and arming the weapon. While the munitions are stacked, a spring-loaded peg projecting from the side of the fuse assembly prevents the tail assembly from arming accidentally, but once the munitions are released the peg falls out of place and allows arming,
On detecting a sudden deceleration from contact with the ground or a target, the third inertial fuse sets off the warhead below. This consists of a 40mm conical shaped charge facing downward. While sufficient to penetrate up to 200 millimeters of armor at an optimal standoff distance, it can only defeat about 60 millimeters on direct contact with the target, where range is relatively short. This is still sufficient, however, to defeat the roof armor on most tanks and armored vehicles.
Chŏl-u 07-nyŏn
Developed in 2007 when production was re-started, the 07-nyŏn variant is identical in the composition of its warhead and explosive charge, but features additional safety measures to increase the likelihood of detonation on impact with the target and reduce the number of dud rounds that may remain behind as unexploded ordnance.
In place of the single safety peg on previous versions, the 07-nyŏn has two smaller pegs, one on either side. Either of these pegs is sufficient to arm the weapon, reducing the likelihood of arming failure exponentially. These pegs are also machined to more precise standards, and are made from a corrosion-resistant alloy, as is the fuse housing itself. This reduces the risk that the peg would remain stuck in the safe position after release, a common problem on early munitions.
For added safety, these pegs also activate 60-second timers, which are connected to the fuse. If the inertial impact sensor is not set off within one minute of arming, an adequate length of time for airburst-released munitions to reach the ground, the weapon automatically self-destructs. Like the pegs, the timers are duplicated for redundancy, and are engineered to a durable standard.
The cylindrical exterior of the Chŏl-u submunition is also scored in a grid form, leaving pre-fragmented weak points to aid in the creation of shrapnel. These fragments are too small and light to penetrate the armor on even lightly protected vehicles, but they have a reported kill radius of five meters against personnel. Extensive testing was conducted during development to ensure that the scored exterior would not collapse under pressure when large numbers of projectiles are expelled from a rocket or shell.
Externally, 07-nyŏn submunitions can also be distinguished by the use of a fabric ribbon rather than metal fins to induce drag and stabilize the weapon in a nose-down direction. In addition to marginally reducing the weight of the unit, this also evaded problems with the metal fins not deploying correctly.
Specifications (Chŏl-u 07-nyŏn)
- Weight: 342 g
- Diameter: 40 mm
- Length to shoulder: 65 mm
- Length overall: 102 mm
- Self-destruct option: yes
- Self-destruct after: 60 seconds
- Explosive: 30.5 g RDX
- Penetration: 60-70 mm (without standoff distance)
Service
The Chŏl-u submunition was developed during the 1970s and introduced to service in 1981, in 152mm artillery shells fired by the JJP-152/27 self-propelled howitzer. It was intended to aid Menghe's defense against an Oyashimese or Columbian amphibious invasion.
Later, in 1995, the Socialist regime unilaterally withdrew rockets, bombs, and shells using the Chŏl-u from service, with the aim of reducing the threat posed by unexploded ordnance to civilians and friendly soldiers. This order was reportedly given under pressure from Choe Sŭng-min himself, and was part of Menghe's broader pivot toward international interventions, counter-insurgency missions, and improving its national image.
In 2005, after the Menghe-Maverica split gravely increased the risk of conventional war on Menghe's borders, the Menghean Army began pressuring the government to return the Chŏl-u to service. Production was restarted in 2007, with the first shell deliveries made the same year.
When reintroducing the round to service, the government mandated that it have an unexploded ordnance rate of below 1%, compared to failure rates of near 50% for rounds produced in the 1980s. To meet these demands, the designers added an additional arming probe to the projectile's fuse unit, revised the fuse design, and added a timer to ensure detonation within roughly one minute of arming. As such, the new projectiles (designated 07-nyŏn) and the old projectiles (81-nyŏn) are technically different designs, but they are identical in weight and dimensions, and the newer versions were introduced after all old stockpiles had been destroyed, so both share the Chŏl-u designation.
Early tests claimed that 99.9% of projectiles detonated properly, either on impact with the ground or one minute afterward. Some defense specialists have questioned these tests, however, suggesting that failure rates under combat conditions may be in the 1-5% range.