JCh-5.5

JCh-5.5 is the final designation given to an interim main battle tank consisting of a JCh-5 hull with an all-new welded turret and bustle autoloader. It is a hybrid design combining features of the JCh-5 and JCh-6, hence its unconventional 5.5 designation. It was also known under the prototype designations S.804 and S.815. All JCh-5.5 tanks are factory rebuilds of existing JCh-5 vehicles, with the old turret removed, the hull internals refurbished, and the new turret installed in place.

Development

S.804

S.804, or Sije Charyang 804 (prototype vehicle 804), was the first design in the evolution of the JCh-5.5. It was developed in the 1990s, initially as a low-priority side project by the Chikai Tank Design Bureau. In 1996 engineers at Chikai pulled a JCh-5D from the assembly line and completed it with the changes spelled out in prior design work, resulting in the first and only operational S.804 prototype. This prototype was never fitted with ERA tiles, as it was only built to prove the viability of the underlying concept, but it would have been fitted with ERA if accepted for service.

The S.804 design was very similar to the JCh-5, owing to its improvised construction, but did incorporate one important difference: a 14-round bustle autoloader installed in a box on the rear of the turret. This allowed the tank to carry full-length unitary 125mm ammunition, which in turn would allow the development of longer APFSDS penetrators. The carousel autoloader was retained, but it would only be loaded with HE, HEAT, and ATGM ammunition. The autoloader was thinly armored, protected against shrapnel and 12.7mm HMG fire but not autocannon or tank fire, but it featured blowoff panels on its roof and the turret rear armor served as a form of protective bulkhead for the crew.

The Menghean Army showed some interest in the new vehicle, but the Ministry of National Defense did not ultimately accept it for service. In particular, MoND evaluators appointed by the Army were concerned about the thin armor around the turret bustle and mechanical problems in loading tests. Some Army staff also advocated for developing an entirely new main battle tank, which would allow them to address many other issues with the JCh-5. This new main battle tank became the JCh-6, which drew heavily on the S.804's basic configuration but was ultimately an entirely different vehicle. With the JCh-6 program receiving MoND approval, the S.804 project was shelved, only to see new life over a decade later as the S.815.

S.815

Sije-Charyang 815 was Chikai's second attempt at designing a JCh-5 variant with a bustle autoloader capable of handling unitary 125mm APFSDS ammunition. Its development process began after the JCh-6 had already entered service, and it made use of many spinoff technologies from the contemporary JCh-8 project, which also produced the JCh-6D main battle tank.

This time around, Chikai designed the S.815 not as a new-production successor to the JCh-6, but rather as a rebuild kit which could keep JCh-5 hulls relevant for decades to come. To maximize efficiency in this regard, the Ministry of National Defense ordered that the first batch of vehicles be based on JCh-5G hulls; as the oldest of the JCh-5 models, the 5G was the most obsolete, especially with regard to its turret geometry and fire control.

Beyond its use of existing hulls, the JCh-5.5 concept regained currency in the early 2010s because of its lighter weight. With reactive armor kits fitted, the JCh-6G1 and JCh-6N reached a mass of over 52 tonnes, and the JCh-6D then in development was on track to surpass 55 tonnes. While this was acceptable on most parts of the land border facing Maverica, the heavier weight and larger size of the JCh-6 made it harder to transport by air or by sea. The Menghean Navy's Marine Infantry were especially interested in the concept of an upgraded JCh-5, as the JCh-6 was so heavy that existing tank landing ships would not be able to transport an entire tank company to the beachhead.

The first S.815 prototype was built in 2012, and tested that year and the next. A small number were delivered in early 2014, seeing service in the Innominadan Crisis with the 2nd Marine Infantry Brigade.

Description

Armament

The main armament of the JCh-5.5 is a 125mm L/46 gun, the same type used on the "G" and "N" models of the JCh-6. The heavier 125mm L/57 of the JCh-6D was also considered, but the L/46 was ultimately selected due to its smaller size, mass, and forward surface area. The gun can elevate to +13.5 degrees or depress to -6.1 degrees, a slightly more limited range than that of the JCh-5.

Like the JCh-6, the JCh-5.5 reloads from a dual autoloader: the bustle autoloader carries 14 unitary rounds, and the carousel carries 28 two-piece rounds, for a total of 42. The hull ammunition storage is left empty to save weight and reduce the probability of a cookoff, though the design of the carousel autoloader results in a high probability of ammunition fire if the hull is penetrated. As on contemporary Menghean MBTs, the main advantage of the dual autoloader arrangement is that it reduces the size of the turret bustle while also permitting a large number of ready rounds to be carried. The bustle autoloader also allows the use of unitary long-rod APFSDS ammunition and the YDCh-73 gun-launched ATGM.

Co-axial armament consists of a single GCh-96Ch 7.5×54mm GPMG fed from a single belt with 3,600 rounds of ammunition. This eliminates the need for the commander to swap out individual ammunition boxes during combat, though the commander must still empty the casing and belt catching tray out the roof hatch. The commander's remote controlled weapon station is identical to that of the JCh-6D and JCh-8, consisting of a 12.7mm GCh-75 linked to the commander's main TV/IR optic with a secondary TV/IR optic for high-angle aiming. There are no backup manual controls for this weapon, and it is mounted on a pedestal behind the commander's cupola instead of rotating around with the cupola.

Protection

Because it reuses the hulls of existing JCh-5G MBTs, the JCh-5.5G has the same hull armor scheme. An additional hardened steel plate was welded on top of the glacis to increase effective armor protection, but the underlying composite armor is retained, despite being several generations behind the newest composite armor schemes of the day.

The new turret has a core hexagonal shape, and concentrates its armor on the front surfaces. The side and rear plates, including the sides and rear of the turret bustle, are only 90mm thick, and protect against 30mm APFSDS but nothing heavier. The turret sides taper inward at 20 degrees, however, meaning that over the forward 40 degree arc the frontal armor protects the entire manned portion of the turret. The bustle is only masked by the turret frontal armor over a narrower 30 degree frontal arc, and is easily defeated by APFSDS fire outside this arc. Blowoff panels on the bustle, however, isolate any ammunition cookoff from the crew, and even at very close ranges and low obliquity enemy IFV and APC fire cannot penetrate it.

The turret frontal armor uses composite modules similar in style to those of the JCh-6D, though the geometry is different and the composite modules are thinner. Unofficial measurements put the line-of-sight thickness at 860mm for a head-on impact and 745mm for an impact at 30 degrees off centerline, and official Menghean sources claim that the base armor is able to withstand two-piece 125mm APFSDS ammunition from T-74 tanks. As on the JCh-8 and JCh-6D, the composite armor modules can be lifted off the turret with the help of a crane, allowing a combat unit to replace damaged armor plates in the field.