Taegisan-class cruiser

<imgur w="300px">kz9Qd4I.png</imgur> Taegisan as she appeared upon commissioning.
Class overview
Name:	Taegisan-class cruiser
Operators:	Greater Menghean Empire
Preceded by:	Madaesan-class cruiser
Succeeded by:	Hasŏlsan-class cruiser
Subclasses:	Obongsan-class cruiser
Built:	1930-1935
In service:	1933-1945
Planned:	4
Completed:	4
Lost:	2
Retired:	2
General characteristics Taegisan, 1933
Type:	Heavy cruiser
Displacement:	12,000 tonnes standard 13,200 tonnes full load
Length:	189.0 m at waterline 194.9 m overall
Beam:	20.4 m
Draught:	6.95 m (normal) 7.16 m (full load)
Propulsion:	4 steam turbines, 100,000 shp total 8 three-drum boilers 2 shafts
Speed:	32.4 knots
Range:	5,000 nm (9,260 km) at 15 knots
Complement:	802
Armament:	4 × 2 200mm L/50 Type 29 naval gun 4 × 2 100mm L/40 Type 28 AA gun 8 × 12.5mm mg (8×1) 4 × 2 550mm trainable torpedo tube
Aircraft carried:	1 × Donghae Type 32 floatplane
Aviation facilities:	1 × catapult, recovery crane

The Taegisan-class cruisers (Menghean 태기산급 순양함 / 泰岐山級巡洋艦, Taegisan-gŭb Sunyangham), known to the allies as the Thai Kee Sahn class, were a pair of heavy cruisers built in the Greater Menghean Empire during the 1930s. Successors to the Madaesan-class cruiser design, they boasted greatly improved combat capabilities, including higher-velocity 20cm guns in three triple turrets, a dual-purpose 130mm secondary battery, and 610mm "long lance" torpedoes licensed from Dayashina. They also incorporated built-in torpedo protection and extensive redundancy, as well as a heavy armor scheme similar to that of their predecessors.

Development

Background

In its initial form, the Selkiö Naval Treaty did not impose limits on the number of cruisers signatories could build, though it did limit them to 12,000 tonnes standard displacement and a main gun caliber of 8 inches or 203 millimeters. The Menghean Navy saw this as a beneficial loophole, as it allowed the construction of large numbers of heavily-armed cruisers to offset Menghe's disadvantage in capital ships. Budgetary constraints and a slow, cautious approach to development prevented the Menghean Navy from fully exploiting this opportunity under the Federative Republic of Menghe government, but after Kwon Chong Hoon's military coup in 1927, the navy received primacy in budgetary decisions and accelerated its construction plans.

The 1931 Avallone Amendment to the Selkiö Naval Treaty closed this loophole by imposing quantitative limits on new heavy cruiser construction. Menghe would now only be able to launch six heavy cruisers (defined as those displacing over 8,000 tonnes standard) between 1 January 1931 and 31 December 1935. With the four Madaesan-class cruisers still on the slipways at the start of this period, Menghe would only be able to lay down two new heavy cruisers until the next round of treaty negotiations. As such, the Imperial Menghean Navy's leadership concluded that unlike the more balanced Madaesans, the next two heavy cruisers would have to achieve as much individual combat capability as possible on a single hull. Moreover, while the Ryangju-class cruisers had complied with the treaty limit as built and the Madaesans came in only slightly over the 12,000-ton limit, the Menghean leadership privately signaled that the Navy was welcome to moderately exceed the treaty tonnage limit as long as the official figure was at least loosely plausible.

This reconsideration also brought about a change in role. While the Ryangju-class cruisers were designed as fast fleet scouts and the Madaesans as general-purpose heavy escorts, the new heavy cruiser class would be optimized for the fleet screening role, either engaging the enemy fleet in skirmishing raids or protecting the battle line against destroyers and other cruisers. Designers quickly settled on an A-XY turret arrangement which would concentrate two-thirds of the ship's main battery aft, allowing it to fight most effectively while skirmishing away from an enemy force. Aft armor would also be strengthened, with the deck armor extending over the steering equipment to prevent the ship from being immobilized while retreating.

Design competition

The earliest design, S5S1, was the most conservative. It followed the same overall A-XY layout as the final design, but used the ubiquitous 100mm L/40 Type 28 dual-purpose gun in six twin mounts for the secondary battery. These mounts lined each side of the ship, with the armored conning tower directly behind the A turret. Standard displacement was estimated at exactly 12,000 tons, though less work was conducted on this design and fewer documents about it survive, so its exact specifications are unknown and likely would have evolved over time.

The Navy leadership evidently found this design underwhelming, and communicated privately that designers should increase its combat capabilities with 13,500 tonnes as the "actual" displacement limit. Around the same time, the Donghae Arsenal announced that it was conducting trials with what would become the 130mm L/60 Type 32 naval gun, which promised greatly improved range and accuracy over the 100mm L/40 Type 28. By mounting a quadruple 130mm gun turret superfiring over the "A" main battery turret, and twin 130mm mounts on the foredeck wings, the designers would be able to concentrate eight 130mm guns firing directly forward, very effective for driving destroyers and other light combatants away from the fleet. Plans using this second weapon, and an enlarged hull size to support it, shared the design prefix S5D, with "D" denoting "large."

Further debate revolved around the powerplant. By the end of 1930, trials with the Ryangju-class cruisers had uncovered serious reliability issues with their Samdo-made high-pressure powerplants, to the point that the Navy was already considering major reconstruction work to keep the ships viable under the total cruiser hull limits of the Avallone Amendment. This led the Navy leadership to strongly encourage the use of a safer powerplant option on the new heavy cruiser class. Countering this imperative was a requirement for high redundancy, as these ships were expected to continue fighting even after sustaining serious damage. Alternating the boiler rooms and turbine rooms would prevent a single underwater shell or torpedo hit from disabling the entire powerplant, but this would also require more compact boilers, as propeller shafts from the forward pair of turbines would have to pass through one of the boiler rooms. To help resolve this issue, design work was divided into S5D1, which arranged eight boilers in separate rooms forward of the turbine rooms, and S5D2, which alternated the boiler and turbine spaces. Less work was conducted on S5D2, as the problem of propeller shafts passing through the aft boiler room proved difficult to accommodate; this had been done successfully on the Madaesan class, but only at the cost of raising the boilers in the hull, resulting in a tall citadel over the machinery. Designers also concluded that S5D2's machinery space issue could only be solved by either lengthening the hull (and thus further driving up displacement) or thinning the torpedo protection (and thus negating the survivability benefits of alternating the boiler and machinery spaces). Work on design S5D2 was terminated in late 1931.

Design S5D1, though the favorite so far, had its own share of problems. Like S5D2, it also had a "stepped" citadel that added a new deck over the machinery, mainly due to the use of tall Donghae Y-type boilers. This added to the ship's weight, and especially to weight high up in the hull, creating problems with stability. The lowermost deck in the hull was also very short, and it seemed the gyroscope and other below-deck machinery spaces would have to be very compact. This culminated in a major redesign, designated S5D3. Key to S5D3 was the use of M-type boilers, which made better use of the rectangular dimensions of the boiler room while also achieving a more efficient superheating cycle. Operating pressure would still be within familiar limits, so the new boilers would not run the same reliability risks. This change of powerplant, along with the relocation of some uptake trunking outside the citadel, enabled a major reduction in the height of the machinery spaces, and by extension, a new citadel layout. The designers built on these benefits by switching from a stepped-deck to a flush-decked design, which, combined with lowering the belt armor over the machinery spaces, resulted in increased structural strength and improved stability. These, in turn, carried forward into improvements in protection and structural strength elsewhere in the ship. As a result of the new deck arrangement, the fore and aft sections of the main armor belt were now somewhat taller, but this was more than counterbalanced by gains elsewhere. The powder magazines were also still located one deck below the waterline, providing good protection from penetrations at close range, and the lowermost deck in the hull was now taller and could accommodate more equipment. Crew accommodation and storage space suffered somewhat from the loss of a deck, but remained relatively generous compared with other Menghean cruisers, especially for a ship that would mainly operate on short sorties rather than long patrols.

Construction and modification

Satisfied with these changes, the Navy leadership selected design S5D3 as the basis for the new cruiser in mid-1932, and ordered two ships to be laid down before the end of the year. The contracts were awarded to the Kimhae Capital Yard and the Wihae National Defense Yard, which had achieved good construction times on the Madaesan-class cruisers. Navy leaders set the ambitious schedule for the completion of these ships, budgeting 500 days for construction and 400 days for fitting-out. This ambitious requirement would bring the new heavy cruisers into service before the middle of 1935, the year by which the national leadership hoped to be prepared for a war with the Casaterran powers.

This schedule soon proved overly ambitious. Due to delays in launching the Madaesan and Munsusan, Taegisan was laid down on 18 October 1932 and Illaksan on 23 November of the same year. The somewhat radical new design, a major departure from the Madaesan class, imposed further delays, as did the extensive use of new equipment systems throughout the ship. A new twist arose after Dayashina agreed to license the 610mm "long lance" torpedo to Menghe. As a long-ranged, hard-hitting weapon, this was well-suited to the Taegisans' intended fleet screening and skirmishing role, but the entire main deck would have to be redesigned to accommodate the larger launchers and the entirely different reloading system. One upshot of these delays is that the ships would enter service after Menghe had withdrawn from the Selkiö Naval Treaty, making the discovery of their true displacement less of a concern. Based on these new considerations, the Navy authorized further modifications of the Taegisan design during construction, including the addition of new small-caliber anti-air guns during fitting-out, a response to the surprisingly persistent threat of land-based air attacks during the Innominada campaign.

Design

Armament

The main battery of the Taegisan-class cruisers consisted of eight 200mm L/50 Type 29 naval guns in four two-gun "G-type" turrets, the same arrangement used on the preceding Madaesan class. Maximum range was 29,200 kilometers, and rate of fire 3 to 4 rounds per minute. Ammunition stowage totaled 200 complete rounds per gun, a mix of armor-piercing, high-explosive, and special anti-submarine shells and segmented powder charges. The turrets themselves were protected by 200mm of armor on the face and 150mm of armor on the sides, with 150mm barbettes.

In contrast to the Madaesans, which had been armed with six individual 100mm high-angle guns for anti-air defense, the Taegisans were designed with eight 100mm L/40 Type 28 anti-air guns in four twin mounts. Obongsan, the last ship in the series, was modified during construction and carried a third pair of twin guns flanking the aft mast. As built, the first three ships had a small-caliber AA armament of eight single 12.5mm machine guns, but this was steadily improved over the course of the war to include an array of Type 38 anti-aircraft guns.

Torpedo armament underwent a modest reduction during the design process, from four triple to four twin tubes, two sets on each side. These fired the extended-range 550-millimeter Type 23-II torpedo, which had a range of 11,000 meters at its lowest speed setting of 31 knots. Eight additional on-board reloads were carried.

Protection

<imgur thumb="yes" w="300" comment="Cross-section scheme of the armor scheme on the Taegisan; note the thick belt and deck armor and the torpedo protection.">OGxpKoP.png</imgur> The above-water armor scheme of the Taegisan-class cruisers was very similar to that on the preceding Madaesans. The main armor belt was 150 millimeters thick, running along the outside of the ship from the forward magazines to the aft ones. The deck armor was 75 millimeters thick, again covering the magazines, engine space, and internal control rooms. As on the Madaesans, the citadel and armor belts only extended a short distance above the waterline, providing good protection against critical hits from relatively short distances but little protection against flooding from small-caliber hits just above the waterline.

Underwater protection, by contrast, was very different. The torpedo defense system was directly contained within the streamlined hull, rather than being added outside in the form of anti-torpedo bulges. It consisted of a 50-millimeter armor plate which extended vertically from the bottom of the hull at a distance of roughly 1.5 meters from the outer layer. At about 4 meters above the base of the hull, this torpedo bulkhead curved outward to meet the bottom of the main armor belt. This created a pocket of watertight air compartments between the bulkhead and the water outside, with a layer of fuel storage tanks on the inner side. The designers anticipated that this configuration would divert the air from the torpedo explosion upward and outward, minimizing the risk of flooding in the citadel and reducing damage to the layer of fuel tanks. A similar torpedo protection scheme would be applied to some later treaty battleship proposals, though ultimately the Hyangchun-class battleships used an angled belt extending deep below the waterline.

Maneuverability

<imgur thumb="yes" w="500" comment="Color-coded lengthwise cross-section showing the internal systems and armor.">BmAFCnj.png</imgur> The powerplant used in the Taegisan-class cruisers was a direct carry-over from that on their predecessors: eight oil-fueled boilers hooked up to four geared steam turbines, with a total output of 100,000 shaft horsepower. In the construction of the new class, the designers made some minor changes to the machinery in an effort to squeeze more out of the displacement limit, shaving down thicker parts and using lighter alloys for some components. This succeeded in reducing the overall weight of the powerplant assembly by 3.6% while keeping maximum output constant.

The designers of the new class had hoped that by streamlining the hull they could achieve greater gains in speed over the Madaesan class despite limiting themselves to the same displacement and power. The higher length-to-beam ratio in particular was expected to increase efficiency. Actual trials, however, revealed that at normal displacement the Taegisan could only reach 32.4 knots, a fifth of a knot faster than the Madaesan and still two knots slower than most treaty-limit cruisers.

This tradeoff primarily reflected the insistence of the then-current IMN leadership that all heavy cruisers possess thick enough armor to withstand 8-inch shells from other heavy cruisers over a generous span of possible combat ranges. Only on the following series of Hasŏlsan-class cruisers would the Navy's new leadership turn its attention to speed, even then retaining fairly generous citadel and torpedo protection.

Ships in the class

In keeping with the tradition which the Madaesans started, all four ships in the class were named after mountains, and thus all of their names include the final character "san" (山). Obongsan, completed after war with Sylva had broken out and after Menghe withdrew from the treaty limitations, was completed with an additional pair of twin 100mm anti-air guns aft, as well as separate fire-control towers for them, and is sometimes considered a unique subclass.

Name	Name (Stuart-Lavender)	Mengja	Laid down	Commissioned	Fate
Taegisan	Thai Kee San	泰岐山	1930	1933	Under conversion to an anti-aircraft cruiser beginning in December 1943; scrapped in 1946.
Munsusan	Moon Soo San	文水山	1930	1934	Sunk by Columbian aircraft at the Battle of Swartzburg in October 1940.
Johangsan	Cho Hang San	鳥項山	1931	1934	In drydock between 1944 and 1945; scrapped at the war's end.
Obongsan	Oh Pong San	五峰山	1932	1935	Sunk by HMS Warchild at the Battle of Hathi Point, 1940.

Operational history

Khalistan campaign

All four ships saw combat at the Battle of the Portcullia Strait, where they escorted the First Battleship Division (consisting of the two Anchŏn-class battleships). None of them took serious damage, as the battleships drew most of the fire, and they were able to support the Axis landings on Portcullia and Khalistan proper in the following months.

As Menghe had entered the war against New Tyran, Dayashina issued the IMN a production license for the Type 93 torpedo in 1938, and in January 1940 the four cruisers were taken into port for repairs and refitted with twin launchers for the new weapon. They also had their medium-caliber AA armament substantially improved, through the addition of twin mounts for the Type 38 anti-aircraft gun.

The Third Cruiser Division saw combat again at the Battle of Hathi Point, where they once again confronted the Tyrannian battleship HMS Warchild. The Johangsan was absent for this engagement, as she had sustained bomb damage before the operation began and had to remain in port for repairs. Due to poor reconnaissance and nighttime conditions, the commander of the Menghean cruiser column did not initially recognize that HMS Warchild was among the attacking ships, and failed to coordinate his defense properly. Obongsan was lost during the engagement, with Taegisan and Munsusan escaping under the cover of darkness. Taegisan sunk one ship, the light cruiser HMS Dagger, and Munsusan claimed to have disabled the HMS Centurion even though the damage to the latter was actually fairly minor.

Anti-aircraft conversion

By 1943, the IMN concluded that the two surviving Taegisan-class cruisers were too slow for independent operations as cruisers; certain Columbian battleships could even overtake them. Throughout 1942 and 1943, they had mainly served as escorts for aircraft carriers, with Johangsan taking severe damage from dive bombers in the process. In order to improve their effectiveness in the new role, the Navy ordered that both ships be rebuilt as anti-aircraft cruisers during their repairs.

The general scheme of this plan was to remove the twin 200mm turrets and replace them with dual-purpose quadruple (or "double-twin") turrets mounting the 130mm L/55 Type 32 naval gun. These would fit atop the original barbettes and hoist ammunition from the below-water magazines. Medium-range anti-aircraft armament would also be improved, through the addition of stabilized, water-cooled quadruple 37mm AA guns. Sources disagree on whether the torpedo tubes would have been removed or retained in this configuration.

The original proposal called for the reconstruction of both ships to be completed before the end of 1944, but due to material shortages and the collapse of Menghe's wartime economy, neither conversion was finished by the war's end. Taegisan, which had been taken into drydock with only minimal damage, was fitted with two of the new turrets by the time of Menghe's surrender, but neither was operational; work on Johangsan had barely progressed at all, as no suitable drydocks were available.

See also

• Sŏnsan-class destroyer