Sunchang-class cruiser

<imgur w="300px">BHT7dYw.png</imgur> Sunchang during her first (and only) year of service.
Class overview
Name:	Sunchang-class cruiser
Operators:	Greater Menghean Empire
Preceded by:	Ichŏn-class cruiser
Succeeded by:	Boryŏng-class cruiser
Built:	1931-1937
In service:	1935-1941
Planned:	5
Completed:	5
Lost:	5
General characteristics Sunchang, 1935
Type:	Light cruiser
Displacement:	6,290 tonnes standard 6,960 tonnes full load
Length:	175.5 m at waterline 180.6 m overall
Beam:	15.7 m
Draught:	5.47 m (normal) 5.64 m (full load)
Propulsion:	4 steam turbines, 80,000 shp total 12 three-drum boilers 6 shafts
Speed:	35 knots
Range:	4,000 nm (7,400 km) at 15 knots
Complement:	435
Armament:	4 × 2 150mm L/50 Type 32 naval gun 4 × 2 100mm L/40 Type 28 AA gun 16 × 12.5mm mg (4×1, 3×4) 4 × 3 550mm trainable torpedo tube
Armor:	Machinery belt: 50mm Magazines: 25mm Deck: 20mm Conning tower: 75mm
Aircraft carried:	1 × Donghae Type 32 floatplane
Aviation facilities:	1 × catapult, recovery crane

The Sunchang-class cruisers (Menghean: 순창급 순양함/ 淳昌級巡洋艦, Sunchang-gŭb Sunyangham) were a group of five light cruisers built in the Greater Menghean Empire during the 1930s. They were known to the Western Allies as the Soon Tsang class. Unlike the Taean and Jinan classes before them, which were intended to engage other light cruisers, the Sunchang-class vessels were designed as dedicated flotilla leaders and destroyer hunters. As such, they were built for very high speeds, but their minimal armor protection was only sufficient to stop destroyer-caliber shells.

During the early years of the Pan-Septentrion War, the cruisers saw extensive action, both as destroyer squadron flagships and as light escorts for larger fleets. Combat experience soon underscored problems with the light armor and minimal torpedo protection. All five ships were lost before 1942: three to torpedoes, one to surface gunfire, and one to a combination of gunfire and torpedoes.

Background

Under the Septentrion Nine-Power Naval Treaty, Menghe was limited to a maximum total cruiser tonnage of 204,000 tonnes, of which 96,000 tonnes could have main battery guns with a caliber in excess of 155 millimeters. In an effort to make the most the treaty restrictions, the Greater Menghean Empire laid down two Taean-class cruisers and two Jinan-class cruisers, each one built with triple 150mm gun turrets but able to be refitted with twin 200mm gun turrets instead.

Both ship classes had respectable armament and armor, but in terms of speed, they were lacking; Taean had a top speed of 31.6 knots, making her possibly the slowest cruiser of her generation, and the Jinan subclass could still manage just 33.7 knots, slower than many purpose-built heavy cruisers. This effectively prevented the Taeans and their cousin ships from serving as flotilla leaders, as they could not keep up with Menghean or foreign destroyers at top speed. Additionally, the ships' A + XY turret layout meant that they could only use one-third of their guns while firing directly ahead of them, which was not ideal for pursuing light surface combatants.

To address these problems, the Imperial Menghean Navy leadership decided to invest in the construction of a "true" light cruiser class. Using the allotted tonnage available, the new class would consist of five ships and would replace the eight aging Janghŭng-class cruisers. High priority was given to speed, a response to the development of faster destroyer classes in other major naval powers, and flotilla command facilities were added to the requirement early on. These priorities entailed sacrifices in armor, leaving the resulting Sunchang class very poorly protected against anything heavier than destroyer-caliber gunfire.

Description

Armament

The Sunchang-class cruisers carried a main battery of eight 150mm L/50 guns in four twin turrets. These were the same gun models used by the Taean-class cruisers in their as-built configuration. The guns were not individually sleeved, and could not fire or elevate independently of one another, a configuration chosen in order to save space and weight. The exceptionally close spacing of the guns was found to create problems with dispersion, as the muzzle blast from each gun interfered in the flight path of the other gun's shell; delayed-trigger coils were introduced in 1937 refits to slightly space out the firing of each gun, which reduced dispersion by 24% in testing.

The 150mm guns had a maximum range of 25,630 meters at an elevation of 44.5 degrees. Their turrets allowed them to elevate to 55 degrees for anti-aircraft fire using time-fused high-explosive shells; the fire-control system mounted atop the conning tower could direct the guns at aerial targets. Turret traverse (14 degrees per second) and rate of fire (6 rounds per minute) were adequate for a surface-to-surface weapon, but in service they were found to be inefficient against aerial targets, especially as the guns had to be brought between -5 and +20 degrees of elevation in order to be reloaded.

The dedicated anti-air battery consisted of eight 100mm L/40 Type 29 guns in four twin-gun open-backed turrets, two on each side. Fire-control towers were located on either side of the large trunked funnel. Maximum surface range with these weapons was reportedly 16,670 meters, and rate of fire was 10-12 rounds per minute. Small-caliber anti-aircraft protection consisted of four single 12.5mm machine guns and three quadruple 12.5mm mounts, the latter appearing on only a few other ship classes of the period; these were found inadequate in range, and during subsequent refits the surviving ships were refitted with Type 38 anti-aircraft guns.

For defense against heavier ships, the Sunchang-class cruisers carried a total of twelve 550mm torpedo tubes, with two triple mounts on each broadside. These fired the extended-range Type 23-II torpedo. No onboard reloads were intended in the initial design, but all ships were fitted with torpedo reload racks along the superstructure behind the funnels during the war. This arrangement left the torpedoes exposed to shrapnel and small-arms fire, and may have contributed to the fire aboard the Sŏngju which preceded her sinking.

Propulsion

The cruisers' propulsion was somewhat more impressive. Twelve oil-burning water-tube boilers fed steam to four turbines just aft of them, each one driving a single shaft. Maximum rated output was 80,000 horsepower in total. At 2,387 tonnes, this machinery arrangement comprised more than a third of the hull's normal-load displacement. Cruise range was 4,000 nautical miles at 14 knots, sufficient to lead destroyer formations to the furthest extent of their range or take part in commerce raiding expeditions in the Helian Ocean.

On pre-commissioning trials, the Sunchang reportedly reached a speed of 37.2 knots, exceeding her designers' expectations. This speed, however, was achieved with reduced fuel, ammunition, and other stores, reducing the ship's displacement in the water and thus her drag. Top speed with a normal combat load was closer to 35 knots in practice, still impressive for a ship of her type and adequate to pursue most contemporary Sylvan and Tyrannian destroyers. It was also adequate to outrun most contemporary heavy cruisers, an important challenge given the ship's poor protection.

Protection

In order to achieve such impressive speed, the Sunchang-class cruisers traded away all but the bare minimum in protection. The design was repeatedly revised during the development process to achieve higher speed, each time by shaving down the armor belt. In the final iteration of the design, the main armor belt was 50 millimeters thick, and it only covered the boiler and machinery spaces. The magazines were located below the waterline, underneath a 20-millimeter deck, with a deck of the same thickness over the citadel, and the fore and aft transverse bulkheads were 25 millimeters thick, with a 50 millimeter box over the steering machinery. Main battery armor was similar in thickness, with 75 millimeters of armor on the turret faces, barbettes, and barbette stalks, 50 millimeters on the turret sides, and 20 millimeters on the turret top and rear.

Underwater protection, meanwhile, was almost nonexistent. Sections of the bow and stern could be sealed off into watertight compartments, and the machinery spaces were divided by seven transverse bulkheads, but apart from a thin double hull configuration to protect against minor damage and contain the oil bunker, the ships had no protection against mines or torpedoes. This shortcoming had to do with space as well as weight; even after Menghe withdrew from the Septentrion Nine-Power Naval Treaty, the Imperial Menghean Navy determined that the added drag from anti-torpedo bulges would bring about an unacceptable decrease in speed.

This armor scheme was barely sufficient to protect the ship's vital components against low-velocity 4-inch and 5-inch shells at medium to long ranges, consistent with the ships' intended role as destroyer leaders and destroyer hunters. Even then, hits by high-explosive shells forward or aft of the small all-or-nothing citadel could lead to flooding in the un-armored sections.

Other features

Like the Ichŏn and (refitted) Gijang classes, the Sunchang-class cruisers were built with a centerline catapult carrying a single floatplane for reconnaissance. This was meant to support their role as a forward screen for the fleet, and represented the only aerial reconnaissance available when operating alone as the flagship of a destroyer squadron. Initially the seaplane used was the Donghae Type 32 floatplane, but from 1937 onward this was replaced with a Namtong Type 36 floatplane. Both were single-engine, twin-float biplanes which lacked folding wings and had to be stored in the open.

For further support in the squadron flagship role, the Sunchang-class cruisers had a dedicated command room on the lowermost deck of the bridge structure. The command facilities were more or less minimal, but sufficient for directing the 6-8 destroyers which would have accompanied her as squadron leader.

Unlike many other Menghean cruiser designs of the interwar period, including the Taean and Jinan classes, the Sunchangs were built with sonar and hydrophones for anti-submarine warfare and could carry two racks of 10 depth charges with 20 more stored under the aft turrets. This was especially surprising given the overwhelming focus on making the most efficient use of hull space, though the sonar and equipment rooms were located outside the armored citadel. The inclusion of sonar was likely intended to help these ships detect incoming submarines when operating as part of a fleet's forward screen, or when leading an offensive destroyer squadron; most interwar Menghean destroyer classes lacked sonar equipment and had to rely on direction from other vessels, a method which proved highly inefficient in practice.

Ships in the class

In all, five Sunchang-class destroyers were laid down and all were completed. Like other Menghean light cruisers, they were named after prefectures.

Name	Name (Stuart-Lavender)	Mengja	Laid down	Commissioned	Fate
Sunchang	Soon Tsang	淳昌	1931	1934	Sunk by Sylvan torpedo bombers in 1935.
Chunchŏn	Tsoon Tsohn	春川	1932	1935	Sunk by Tyrannian gunfire in 1940.
Janghŭng	Chang Hung	長興	1933	1936	Sunk by torpedo from a Maverican destroyer at the Battle off Litzheim, January 1938.
Sŏngju	Sohng Chu	星州	1933	1936	Sunk by a combination of gunfire and torpedo damage during the Evacuation of Santiago, November 1938.
Nonsan	Non San	論山	1934	1937	Torpedoed by a Columbian submarine in 1941.

Skeptical designers' concerns about protection were apparently well-placed. All five ships in the class were lost before the end of the year 1941. In three of these cases, the cause of sinking was torpedo damage, while in one it was gunfire; the remaining ship, Sŏngju, was lost to a combination of torpedo and gun damage.

The first ship in the class, Sunchang, was lost in the second month of the war. On June 14th, 1935, she was attacked by Sylvan land-based torpedo bombers from while patrolling the coast of Innominada. A single 18-inch torpedo struck the side of the hull just underneath her seaplane catapult, opening a hole underneath the main belt armor. This set off flooding in both of her turbine rooms, shorting out the machinery and bringing the ship to a standstill. The torpedo boat formation she was leading regrouped nearby, initially planning to tow her to safety, but the flooding continued to spread through the machinery spaces, and in the end her captain issued the order to abandon ship. She was the first Menghean warship of above 2,000 tonnes lost in the war.

The loss of the Sunchang barely a year after her commissioning prompted an internal review in the Navy's design division over the sources of the problem. One immediate issue was the minimal AA suite, which apart from the 100mm and ineffective 150mm flak turrets consisted entirely of 12.5mm-caliber weapons. These lacked the range to engage aircraft dropping torpedoes from a distance, a problem which interwar tests with slow, non-maneuvering towed drogues had failed to identify. In the interim period, many Menghean ships were retrofitted with previously mothballed 2-pounder pom pom guns, and design work began on the Type 38 anti-aircraft gun. At a deeper level, the designers perceived the simultaneous loss of both turbine compartments as a major threat, and modified subsequent Menghean warships to distribute the turbines between two or more compartments so that the ship could still maneuver if one were flooded or damaged by shellfire.

Janghŭng succumbed next, in early 1938. Along with her sister ship Sŏngju, she was escorting the First Fleet to attack the Maverican fleet anchored at Litzheim. As news of the incoming formation went out, the Maverican Navy sent out a squadron of destroyers in an effort to buy time for the battleship and cruisers to withdraw. Janghŭng opened fire on the incoming light craft, claiming one destroyer as a kill. Three 4-inch shells struck her hull, but they impacted well above the waterline, causing only minor damage. Disaster struck only as a 21-inch torpedo impacted near the forward magazines, failing to detonate them but tearing off most of the bow in the warhead's explosion alone. Flooding rapidly, she began to sink bow-first, breaking in two as her stern rose into the air. Only 35 men from her crew of 453 were rescued.

Sŏngju survived the Battle off Litzheim without sustaining any serious damage, and transferred to a temporary anchorage at Lyon after that city fell to Menghean forces. During the Evacuation of Santiago, which followed the Battle of the Portcullia Strait, she took part in the Menghean operation to intercept the Sylvan transport ships leaving Innominada, but owing to poor reconnaissance her formation ran into a larger Sylvan surface force. Sŏngju took multiple 5-inch and 6-inch shell hits above the waterline, and while only two penetrated the citadel, a larger explosion under her seaplane catapult - possibly set off by the ignition of aviation fuel or stored torpedoes - started fires across her stern half. As the damage control team rushed to put the raging blaze under control, a torpedo struck underneath her bridge, detonating the forward magazines and tearing the ship in half. Debate continues over whether the shellfire would have been sufficient to cripple her, as she was already operating at reduced speed when the torpedo struck.

After the loss of three ships in the class, Chunchŏn and Nonsan were removed from fleet screening duties and assigned to lead destroyer squadron operations. They were also refitted with better anti-aircraft weapons, including the Type 38 anti-aircraft gun. These ships saw very little action in 1939, and they did not take part in commerce raiding missions, as some in the Navy leadership proposed. The Chunchŏn and her destroyers encountered a group of Tyrannian cruisers in the evening of April 5, 1940 in Henderson's Passage, between the Acheron Islands and Khalistan. Chunchŏn scored a few hits, but suffered many, as 6-inch and 8-inch shells tore through her thin belt armor and left her immobilized. She sank shortly after the Tyrannian cruisers withdrew to seek reinforcements.

This left Nonsan, the last ship completed, as the last one in service. Relegated to rear-line patrol and escort duties, she saw little combat; in fact, she was the only ship in the class never to fire her guns in anger (Sunchang bombarded Innominadan coastal positions at the outbreak of the war). In July 1941, she encountered a hostile submarine near the Strait of Portcullia and pursued it, dropping depth charges over its last known position; but the submarine, OSS Trout, moved out of her path after entering the cruiser's blind zone, and fired four torpedoes from her aft tubes while retreating. Two of these struck the Nonsan on her port side. Unable to contain the flooding, her crew abandoned ship, and were rescued by an anti-submarine patrol ship in her formation.

See also

• Sangdong-class destroyer
• Taegisan-class cruiser