Ryangju-class cruiser

The Ryangju-class cruisers (梁州級巡洋艦, Ryangju-gŭp Sunyangham) were a pair of cruisers built for the Menghean Navy in the late 1920s. Carrying 200mm guns but lightly armored and optimized for speed, they were initially designated as light cruisers, but after a reconstruction in the mid-1930s the Menghean Navy reclassified them as heavy cruisers. Both ships participated in the Pan-Septentrion War.

Development

Designed after the Selkiö Naval Treaty limited cruisers to a standard displacement of 12,000 tonnes and main guns of 8 inches (203mm) in caliber, the Ryangju-class cruisers were Menghe's initial answer to these limits.

Reasoning that Menghe would not be able to match its adversaries in terms of the overall number of hulls produced, the Menghean Navy ordered the design of a treaty-limit cruiser that would have enough speed to outrun its adversaries, giving the ship or its division the ability to withdraw from unfavorable engagements. Though unable to stand directly against enemy heavy cruisers, such a ship would be useful as a fleet scout, or as a commerce raider intercepting cargo ships traveling between Dayashina and its Meridian colonies. Similar to the original principle of the battlecruiser, this would result in a ship able to outrun anything it couldn't fight (battleships, battlecruisers, other heavy cruisers) and withstand gunfire from anything it couldn't outrun (fast light cruisers, destroyers).

As with other Menghean ships of the era, one of the qualities the Navy sacrificed was range, on the reasoning that these ships would mainly make short round-trip voyages from Menghe's coast. Armor thickness was also reduced to 75mm on most horizontal surfaces, providing protection against the 14 cm/50 3rd Year Type naval gun on Dayashinese light cruisers but little else. In spite of the fact that these ships would spend much of their time chasing torpedo-armed vessels, little thought was given to torpedo protection, with the ships kept sleek to buy additional speed.

Ryangju was laid down at the Hyŏngnam-Kimhae Naval Yard on 17 September 1926, and launched on 28 April 1929, with construction taking longer than the Navy had planned due to the considerable increase in size and complexity over the preceding Ichŏn-class cruisers. Trials were accelerated in an effort to compensate for this, with both ships brought into service before the end of 1930.

Design (as built)

Layout

The Ryangju-class cruisers used a fairly conventional layout for the time, with an AB-XY twin turret configuration and a hull step just over 1/3 of the way along the ship's waterline length. Though the machinery spaces were cramped, accommodation and workspace room was relatively generous, especially in comparison to the notoriously cramped Ichŏn class. Command facilities, however, were minimal in the as-built configuration, with a fairly minimal wheelhouse and compass platform forward and an open-topped steering platform aft. This is primarily because the ships were intended to function as scouts and commerce raiders rather than flagships for destroyer squadrons, a role assumed by other light cruisers.

Along with being the largest built yet, the Ryangju-class cruisers were also the first Menghean cruisers to be designed with floatplane facilities. A single centerline catapult over the turbine spaces supported a Donghae Type 30 reconnaissance floatplane. On-board maintenance facilities were minimal, and no hangar was incorporated into the design, with the floatplane stored on the catapult at all times.

One minor innovation introduced on the Ryangju class was the use of hinged rather than rotating davits to carry four of the ship's boats. Originally conceived as a measure to save space and improve the firing arcs of the ship's secondary battery, this introduced a crane model that would appear on several subsequent Menghean warship classes.

Armament

The main battery of the Ryangju-class cruisers consisted of four 200mm L/50 Type 25 naval guns in four Type 26 twin turrets. To save weight and volume (and hence armor weight), these guns were mounted close together, sharing the same sleeve and cradle. This complicated shell handling, which reduced the rate of fire, and it also had a negative impact on accuracy due to interference between the shells in flight. Ammunition storage was 140 rounds per gun, evenly distributed between the fore and aft magazines.

The secondary battery consisted of six 100mm L/40 Type 26 AA guns in unshielded single mounts. Though primarily for anti-aircraft use, these could also engage surface targets, with anti-surface directors on the sides of the forward tripod mast. High-angle director-rangefinders were on two separate raised platforms between the Number 2 and Number 3 funnels. For short-range air defense, these were supplemented by four manually-loaded 37.5mm L/45 Type 29 AA guns in Type 29 single mounts, and four water-cooled Type 26 12.5mm machine guns.

Torpedo armament consisted of two Type 26 triple launchers for the Type 23 550mm torpedo family. Three reloads were carried for each torpedo tube, in above-water storage on the sides of the aft superstructure. A fixed crane structure and tracked trolley assisted with reloading at sea, though the torpedoes still had to be reloaded individually and by hand.

Protection

The main armor belt of the Ryangju-class cruisers measured 70mm thick, 133.8 meters long, and 3.5 meters high, covering both the magazine and machinery spaces. The deck armor was 50mm thick, also uniform over these spaces. The conning tower was 100mm thick on all sides and 50mm thick on the roof. The main battery turrets were protected by 100mm of armor on the face and 75mm of armor on the sides, roof, and rear. The barbettes measured 75mm thick as well.

Torpedo protection on the class was effectively nonexistent. Structural steel bulkheads in a double hull configuration provided watertight compartments along the sides of the hull, some of which were used for fuel storage, but both the inner bulkhead walls and the watertight spaces were too thin to meaningfully reduce the flooding caused by a torpedo hit. The machinery spaces were divided into three boiler rooms and two turbine rooms, all separated by watertight transverse bulkheads; but the turbine rooms were placed end-to-end, meaning that a shell or torpedo hit that flooded both of them could immobilize the ship.

Powerplant

At the core of the Ryangju-class design was a large steam powerplant consisting of twelve oil-fired boilers supplying steam to four sets of geared turbines. This was a gamble on several levels. First, the Ryangjus were the first Menghean cruisers to feature an all-oil boiler setup. Previous Menghean cruiser and capital ship classes had featured at least some coal-burning boilers, to provide backup cruising power in the event of a severe oil shortage. Second, in an effort to squeeze out as much speed as possible, the Navy selected an experimental high-pressure boiler design from the private Samdo Engineering Company. Though initial sizing estimates projected that the powerplant would support a 135,000 shp output, Samdo promised 150,000 shp from their boiler configuration, which would bring the top speed to 36.2 knots at normal load conditions—fast enough to overtake Dayashinese light cruisers.

This experimental powerplant suffered from severe reliability issues, which quickly became apparent in the ships' early service life. On trials, the ships failed to reach even their 35.2-knot design speed, and pushing for this speed resulted in damage to the steam plant, especially the piping, which had a tendency to leak jets of superheated high-pressure steam. Minor repairs in 1932 proved inadequate, and the Navy temporarily ordered that the ships limit their speed to 31 knots in order to avoid pushing the powerplant too hard.