Boryŏng-class cruiser

The Boryŏng-class cruisers (Menghean: 보령급 순양함 / 保寧級巡洋艦, Boryŏng-gŭb sunyangham) were a group of five light cruisers built for the Imperial Menghean Navy during the early years of the Pan-Septentrion War. They were conceived as an improved version of the Sunchang-class cruisers, which had been subject to treaty limitations, and followed the same basic layout while carrying improved armor protection.

Design

In basic layout and capabilities, the Boryŏngs bore a strong resemblance to their predecessors and brought only incremental changes. Their engines were somewhat more powerful, and their armor was somewhat thicker, but overall shared the same capabilities and weaknesses. Their role was also identical: they would serve as destroyer squadron leaders and outer screening ships for surface formations, relying on speed to escape anything larger than a destroyer.

Externally, they could be distinguished from the Sunchangs according to the following characteristics: twin funnels of equal size; a mast and catapult between the funnels, rather than behind them; a more pointed bow; and a unique bridge structure with a characteristic "chin," in comparison with the low-set bridge of the Sunchangs. The last three ships of the class (Jongsang, Yŏntan, and Inje) had the aft mast and aft flak turret pair offset further astern, with some changes to the layout of the anti-air mounts, and are sometimes considered a minor subclass.

Armament

The main battery consisted of eight 150mm L/50 guns in twin turrets, following an AB-XY arrangement. To save space, the guns were not individually sleeved and could only elevate and fire in pairs. The turrets themselves were identical to those used on the Sunchangs, though magazine capacity was increased to 120 rounds per gun, and an additional rangefinder was added forward of the "X" turret for further redundancy.

Likewise, flak armament consisted of four twin 100mm L/40 dual-purpose guns in open-backed mounts flanking the funnels, an arrangement seen on both predecessor and successor classes. As completed, the Boryŏng and Gwangpyŏng carried six Type 38 anti-aircraft guns in Navy Type-G single mounts; fire-control and gun number would increase during wartime refits.

Torpedo armament was the only area of notable improvement. The first two ships had the same 550mm triple launchers as the Sunchangs, firing the Type 23-II torpedo, but the Jongsang replaced them with twin 610mm launchers for the Dayashinese "Long Lance" torpedo. These significantly increased the range and hitting power of the cruisers' torpedoes, giving them improved offensive capability against capital ships. Identical launchers were refitted to the two surviving Sunchang-class cruisers, Nonsan and Chunchŏn, in 1939.

Protection

The basic arrangement of the armor scheme on the Boryŏng-class cruisers was carried forward from their predecessors. The turbine and boiler rooms, which extended well above the waterline, were protected by a thin armored citadel, while the magazines were carried below the waterline and had no horizontal protection, only angled sections of deck armor for shells that passed through the water. The thickness of the belt and deck armor was increased, to 75 and 25 millimeters respectively, but even at this thickness it was mainly intended to stop 5-inch destroyer shells and, at retreating angles, 6-inch shells from other light cruisers.

Torpedo protection remained virtually nonexistent; the large machinery spaces were only separated from the water outside by a thin double hull, with oil bunkers flanking the turbine rooms and magazines. The Boryŏngs did, however, bring improvements in internal layout: the "BT-BT" arrangement of boilers and turbines meant that no single torpedo hit could flood both turbine sections and immobilize the ship, a fate which befell the Sunchang in her first month of wartime service. This layout was later carried forward to the Yŏngil-class cruisers.

Propulsion

The powerplant consisted of four steam turbines, each geared to a single propeller shaft. Steam was provided by twelve oil-fueled water-tube boilers in two groups of six. Machinery rooms were separated by transverse watertight bulkheads, but lacked centerline ones. The new arrangement raised maximum power to 100,000 shaft horsepower, which in spite of the increased displacement lifted the top speed to slightly in excess of 35 knots. Cruise range was roughly identical between classes, with official sources claiming 4,000 nautical miles at 15 knots.

See also

• Hanmaesan-class cruiser
• Sangdong-class destroyer