Hasŏlsan-class cruiser

<imgur w="300px">KE2AEei.png</imgur> Hasŏlsan as she appeared upon commissioning.
Class overview
Name:	Hasŏlsan-class cruiser
Operators:	Greater Menghean Empire
Preceded by:	Taegisan-class cruiser
Succeeded by:	Hanmaesan-class cruiser
Built:	1933-1937
In service:	1936-1941
Planned:	2
Completed:	2
Lost:	2
General characteristics Hasŏlsan, 1936
Type:	Heavy cruiser
Displacement:	15,400 long tons standard 17,600 long tons full load
Length:	197.5 m at waterline 203.5 m overall
Beam:	21.5 m
Draught:	8.23 m (normal) 8.57 m (full load)
Propulsion:	4 steam turbines, 150,000 shp total 12 three-drum boilers 4 shafts
Speed:	35.7 knots
Range:	6,500 nm (12,000 km) at 15 knots
Complement:	985
Armament:	4 × 3 200mm L/55 Type 34 naval gun 8 × 2 100mm L/40 Type 28 AA gun 22 × 12.5mm mg (22×1) 4 × 3 550mm trainable torpedo tube
Aircraft carried:	3 or 4 floatplanes
Aviation facilities:	2 × catapult, recovery crane

The Hasŏlsan-class cruisers (Menghean: 하설산급 순양함 / 夏雪山級巡洋艦, Hasŏlsan-gŭb Sunyangham) were a pair of heavy cruisers built in the Greater Menghean Empire around the start of the Pan-Septentrion War. They were Menghe's second-to-last heavy cruiser class to see service, and were designed to carry the maximum armament allowable under treaty restrictions. Consequently, they were also severely overweight, weighing 3,000 tonnes more than their official claimed displacement figure. They were known to the Western allies as the Ha Sohl San class.

In contrast to previous Menghean heavy cruisers, which traded speed and range for armor, the Hasŏlsans were designed for a top speed of 35 knots so that they could catch up with enemy light and heavy cruisers in a pursuing engagement. In return, they made some sacrifices in belt armor and torpedo protection, and were regarded as less structurally sound than their predecessors. The Hanmaesan-class cruisers which followed them used the same general layout, but with strengthened structural components, improved armor, and improved large-caliber anti-air guns.

Development

Menghe's first six interwar heavy cruisers, the Madaesan and Taegisan classes, were built to a fairly conservative configuration, with four twin 200mm turrets, 150mm belt armor, and top speeds of slightly over 32 knots. They were designed for defensive operations, with armament and protection dictated by the need to safely engage foreign heavy cruiser classes at regular combat ranges. Both classes fell within the 12,000-ton limit set by the Septentrion Nine-Power Naval Treaty, and within that limit they were fairly sturdy ships, with good seaworthiness and reinforced internal structures.

As the naval arms race continued into the 1930s, certain figures in the IMN leadership began to doubt the merits of this approach. Contemporary heavy cruiser classes produced in Tol Galen carried twelve 7.5-inch guns in four triple turrets, and the latest cruiser classes built in Dayashina were even heavier, with widespread speculation that they violated the treaty's displacement limits. Naval strategists aligned with Kwon Chong-hoon expressed concern that they were being left behind, and called for a new cruiser class to close the gap.

The naval expansionists got their chance in April 1932, when a purge of the Navy's leadership brought nationalists into key positions. Rejecting an earlier proposal for a well-armored cruiser with nine 200mm guns in three triple turrets, they called for the addition of a fourth triple turret, bringing the main battery to twelve guns. The powerplant was also expanded, with a design top speed of 35 knots, and the armor thicknesses somewhat reduced. Design features from the contemporary Unmunsan-class super-heavy cruisers, including an angled internal armor belt and a bulbous bow, were carried over onto the new ships. The first vessel was laid down in 1933, and the second in 1934, at a time when Menghean and Themiclesian forces were already clashing in Dzhungestan.

The ever-growing speed and armament requirements necessitated steady increases in hull size, even with modest reductions in armor. The designers made a number of efforts to shave off weight, using thinner plating for the upper hull and all-welded rather than riveted construction. Nevertheless, the ships continued to grow in size, and even before their completion foreign naval experts expressed serious doubt that Menghean engineers could fit the required specifications into a hull which sat within the treaty limits. By the time the Unmunsan was commissioned into service, she displaced some 15,500 tonnes at standard load, though by this time the treaty order had already collapsed and Menghe was at war with Sylva.

Characteristics

Armament

The main battery of the Hasŏlsans consisted of twelve 200mm guns in four triple turrets, following an AB+XY layout. These were a different gun type from the main battery of previous Menghean light cruisers, including the Taeans and Jinans, designated 200mm L/55 Type 34 naval gun. They differed chiefly in having a higher muzzle velocity and an improved breech design, and had a comparable rate of fire despite using heavier shells. Higher velocities and flatter travel arcs did lead to reduced deck penetration at any given range, as the shells lost velocity less quickly and descended at shallower angles. The ammunition load was also somewhat light at 120 rounds per gun.

The anti-aircraft armament was the heaviest of any Menghean heavy cruiser to date, with four twin 100mm guns per side in open-backed turrets. Fire-control towers were located on either side of the conning tower, with two more just aft of the funnel. These guns had a high rate of fire and reasonable traverse and elevation rates, but their lackluster range and accuracy limited their usefulness in area defense.

While the Unmunsan was in fitting-out, it was already apparent that the IMN's 12.5mm machine guns lacked the range and stopping power necessary to fend off air attacks, but work on a medium-range anti-air gun was still underway. As a result, both cruisers were completed with mounting spaces set aside for larger anti-air guns, but only carried anti-air machine guns as built. They were finally fitted with Type 38 anti-aircraft guns in October 1938.

Torpedo armament consisted of four quadruple tubes, two on each beam, carrying the 550mm Type 23-II extended-range torpedo. Negotiations to add the heavier Dayashinese "Long Lance" stalled until Menghe entered the war against Tyran, and these weapons were also added during October 1938 refits. In this configuration, the forward launcher pair had a quick-reload rack forward, but the aft pair did not. Below-deck reloads, which were carried for the 550mm tubes, were removed.

Protection

In terms of armor, the Hasŏlsans were somewhat more lightly protected than their predecessors. The upper main belt, which covered the machinery spaces only, was 100 millimeters thick and angled inward at 20 degrees. A 75mm lower belt, also angled, ran beneath it, extending further forward and aft to cover the magazine spaces. The Hasŏlsans were the first Menghean cruisers to omit belt armor above the magazines, which were entirely below the waterline. Deck armor was 75 millimeters thick over the entire citadel, and over the machinery spaces it had "turtleback" edges angled at 20 degrees from the horizontal. Menghean sources claim an "8-inch AP immunity zone" of 18,000 to 25,000 meters with this scheme, though the turtleback armor edges were more vulnerable to descending shells.

Main battery armor was roughly comparable: the turret faces and barbettes were 150mm thick, and the turret sides and hoist stalks 100mm thick. The anti-air guns and torpedo launchers were protected by 10mm shields, which offered modest protection against strafing aircraft and shrapnel. The single fire-control tower for the main battery was protected by 75mm armor, and the conning tower by 100mm armor.

Torpedo protection was also sacrificed in the futile effort to keep displacement at an acceptable level. A 50mm torpedo bulkhead descended underneath the 75mm lower belt, vertical rather than angled to leave more internal space for fuel, ammunition, and machinery. Overall, the air and fuel storage sections on either side were relatively thin, and mainly offered protection against lighter air-dropped torpedoes. The Illaksan would pay for this omission in 1941, when she suffered two 21-inch torpedo hits from a Columbian submarine and sunk after her crew were unable to contain the flooding.

Machinery

Speed was an important element of the Hasŏlsan design. These cruisers were intended to pursue enemy heavy and light cruisers, with a limited capacity to chase off destroyers. Menghean engineers opted for a 150,000-horsepower powerplant, with twelve rather than eight water-tube boilers in a more compact design. These fed steam to four geared turbines, each driving a single propeller shaft. To save space and weight, the turbine and engine rooms were built without the centerline flood bulkhead common on other Menghean warships, and they were mounted in three rather than six transverse engine rooms, yielding further sacrifices in flooding protection. These sacrifices did pay off as intended: Hasŏlsan reached a top speed of 35.7 knots on pre-commissioning trials.

The Hasŏlsans were the first Menghean heavy cruisers to feature a twin rudder design, for increased maneuverability in light of their high speed and increased displacement. The steering gear compartment was located under the waterline and protected by a 75mm armored box with 50mm front and 100mm rear plates. On trials and in service, they showed good responsiveness and maneuverability.

Aircraft

Depending on the mission, the Hasŏlsans could carry either three or four reconnaissance floatplanes: one on each catapult and either one or two on pedestals behind them. Use of the outer pedestals allowed a larger number of planes to be carried, but also severely restricted the "X" turret's field of fire, limiting it to 60 degrees off the bow. This configuration was used for reconnaissance or convoy-raiding missions. Use of a single floatplane on the centerline pedestal allowed a wider field of fire, preferable for combat operations with other floatplane-equipped ships nearby. In either case, stored floatplanes could be pushed along deck rails on their pedestals, or moved and recovered by crane.

Ships in the class

Only two Hasŏlsan-class cruisers were laid down before the outbreak of the Pan-Septentrion War, as further construction would have caused Menghe to exceed its tonnage limit for heavy cruisers. Some documents suggest that the IMN anticipated an expansion or renegotiation of the treaty, but by the time the Illaksan was laid down, it was becoming clear that the treaty order would soon come to an end. The Hanmaesan-class cruisers laid down from 1936 onward followed the basic Hasŏlsan design, but with improved armor and anti-air defenses, and they are generally considered an entirely separate class.

Name	Name (Stuart-Lavender)	Mengja	Laid down	Commissioned	Fate
Hasŏlsan	Ha Sohl San	夏雪山	1933	1936	Sunk by Columbian dive-bombers at the Battle of Swartzburg on 29 October 1940.
Illaksan	Il Lak San	日落山	1934	1937	Sunk by a Columbian submarine on 14 September 1941.

See also

• Unmunsan-class super-heavy cruiser