Hydra-class battleship

Hydra class

Line drawing of the Hydra class battleship
Class overview
Name:	Hydra class
Builders:	Isenstadt Naval Works
Operators:	Arcaenian Navy
Built:	1939–1944
Planned:	4
Completed:	4
General characteristics (as built)
Type:	battleship
Displacement:	64,000 t (63,000 long tons) (standard) 68,000 t (66,900 long tons) (combat) 76,000 t (74,800 long tons) (full load)
Length:	277 m (908.8 ft) (waterline) 286 m (938.3 ft) (overall)
Beam:	39 m (128.0 ft)
Draft:	12.2 m (40.0 ft) (full load)
Installed power:	200,000 shp (150,000 kW)
Propulsion:	16 diesel engines, 4 shafts
Speed:	30 knots
Range:	19,000 nautical miles (35,000 km) at 19 knots (35 km/h)
Complement:	Standard: 2,400 Flagship: 2,800
Armament:	8 × 42 cm (16.5 in) SK L/50 guns 28 × 12.0 cm (4.7 in) SK L/50 guns 40 × 4.0 cm (1.6 in) FlaK L/60 guns 64 × 2 cm (0.8 in) Flak L/70 guns
Armor:	Main belt: 300 mm (11.8 in) Upper belt: 200 mm (7.9 in) Bulkheads: 220 mm (8.7 in) Barbettes: 400 mm (16 in) Turret face: 400 mm (16 in) Conning tower: 350 mm (13.8 in) Decks: 175–200 mm (6.9–7.9 in)
Aviation facilities:	1 Aircraft catapult

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Design

General characteristics

The Hydra class battleships were 277 m (908.8 ft) long at the waterline and 286 m (938.3 ft) long overall. The ships had a beam of 39 m (128.0 ft) and a draft of 12.2 m (40.0 ft) meters at full load. The ships had a designed combat displacement of 68,000 t (66,900 long tons) increasing to 76,000 t (74,800 long tons) at full load. Metacentric height was 4 m (13.1 ft) at full load. The hull was over 90% welded construction and was divided longitudinally into twenty-two watertight compartments and featured a bulbous bow with a triple bottom under the armored citadel. Four bilge keels were also fitted to the sides of the hull to increase stability. Mainly due to their size and wide beam the ships were considered good seaboats and were stable and very maneuverable even in heavy seas. The ships relatively high metacentric height also meant the ships were exceptionally steady gun platforms with a short rolling period. The ships had a standard crew of 130 officers and 2470 enlisted men and were equipped with multiple smaller boats including three picket boats, four barges, one launch, two pinnaces, two cutters, two yawls, and two dinghies

Propulsion

The Hydra class ships were powered by sixteen nine-cylinder double acting two-stroke diesel engines that provided a total of 200,000 shaft horsepower at 450 rpm. Each 225 tonne (248 ton) engine had a 65 cm (25.6 in) bore, a 95 cm (37.4 in) stroke, and displaced 5,423 L (330,945 cu in). The engines were grouped into four sets of four with each set of four engines grouped into two pairs connecting to a hydraulic transmission driving one of the four shafts. The machinery was further split into 12 separate compartments with each engine pair and each hydraulic transmission located in its own watertight compartment. The ship's four three-bladed screws were 4.8 m (15 ft 9 in) in diameter with the center two propellers featuring a controllable pitch and could be feathered when not in use to improve cruising efficiency. The outer shafts also features large skegs designed to strengthen the stern structure. At their rated power of 200,000 shaft horsepower (150,000 kW) the ship's engines provided for a top speed of 30 knots (56 km/h; 35 mph) with an overlord power setting of 220,000 shaft horsepower (160,000 kW) providing a top speed of 31 knots (57 km/h; 36 mph) .Steering was controlled by two rudders which could each be jettisoned with an explosive charge in the event they became jammed. Each ship was designed to carry up to 10,000 t (9,800 long tons; 11,000 short tons) of diesel oil which provided a cruising range of 19,000 nmi (35,000 km; 22,000 mi) at a speed of 19 kn (35 km/h; 22 mph) or 7,000 nmi (13,000 km; 8,100 mi) at a speed of 30 kn (56 km/h; 35 mph). Two oil fired boilers and two exhaust gas boilers where located between the transmissions supplied the ship's with hot steam for various functions. Electrical power for the ships was provided by eight 920 kW DC diesel generators at 230 volts and four 460 kW AC diesel generators at 110 volts for a total of 9,200 kW of electrical power.

Armament

Main battery

The primary armament of the Hydra class battleships consisted of four 42 cm SK L/50 guns mounted in four two-gun turrets, two forward and two aft. The 42 cm SK L/50 gun is 50 calibers long and fired both APC and HE shells weighing 1,220 kg (2,690 lb) at a muzzle velocity of 830 meters per second (2,700 ft/s). The turrets could each rotate 150° to either side of the ship's center-line at 4° per second and could be elevated from -8°(0° for the super-firing guns) up to +40° at up to 12° per second. At maximum elevation the maximum firing range of the guns was 45,000 m (49,000 yd). Training of the turrets was electric while elevation, loading, and all other functions was hydraulic. Traverse and elevation were both controlled remotely using Remote power control (RPC) gear. The loading angle of each gun was fixed at an angle of 2.5° and rate of fire was 2-2.5 rounds per minute per gun, depending on elevation. As was common with all Arcaenian naval guns of the era the guns used a horizontally sliding wedge breech block. The breech was fully sealed with a 127 kg (280 lb) brass (later mild steel) cartridge case that contained a 180 kg (400 lb) smokeless RPC main propellant charge which was supplemented with a bagged fore charge containing an additional 187 kg (412 lb) of RPC propellant. The guns featured a removable loose liner that was expected to last 200 rounds before replacement. The main battery was supplied with 960 rounds, or 120 rounds per gun with the usual division being 80 APC round and 40 HE rounds.

Secondary battery

The secondary armament of the Hydra class was twenty eight 12.0 cm (4.7") SK L/50 dual-purpose guns housed in fourteen twin turrets, seven located along each side of the superstructure. Originally designed a destroyer weapon these guns were added to the Hydra class to give them a dual-purpose secondary armament capable of effectively engaging both air and surface targets. Each turret could be depressed to -10° degrees and elevated to +80°. The guns used single piece ammunition weighing 41 kg (90 lb) and fired HE shells weighing 24 kg (53 lb) at a muzzle velocity of 900 meters per second (3,000 ft/s). At 45° degree elevation the maximum surface ranges of the guns was 20,600 m (22,500 yd). Maximum anti-aircraft ceiling of the guns was 14,000 m (15,000 yd) at an elevation of 80°. The guns featured a loose-liner and a semi-automatic horizontally sliding breech block which opened automatically under the force of recoil. Integral electro-hydraulic shell hoists with automatic fuze setters and electro-hydrauli power rammers for each gun were fitted to each turret which allowed for loading at any elevation. Like the main battery turrets each of the secondary battery turrets was fitted with Remote power control (RPC) gear with each twin turret was trained using a 4 PS hydraulic motor which could train the entire turret at 25° per second and the twin guns were elevated by a 10 PS hydraulic motor which could elevate both guns at a range of 15° per second. The guns were designed to fired nose fuzed HE rounds which could be fitted point detonating (PD), mechanical Time (MT), and later proximity (VT) nose fuzes. Rate of fire was 15-20 rounds per minute for each gun and ammunition storage was 50 ready rounds per gun in the turret with an additional 500 rounds per gun located in each turret magazine.

Anti-aircraft battery

The ships close range air defense armament consisted of forty 4.0 cm (1.6 in) FlaK L/60 guns and sixty-four 2 cm (0.8 in) Flak L/70 guns. The 4.0 cm guns were placed in twenty twin mounts while the 2.0 cm guns were placed in twelve quadruple mounts distributed around the superstrucutre. The 4.0 cm (1.6 in) FlaK L/60 guns fired an 0.93 kg (2.1 lb) high explosive tracer (HE-T) shell at a muzzle velocity of 850 meters per second (2,800 ft/s) to a maximum range of 9,600 m (10,500 yd) with an effective AA ceiling of 6,200 m (6,800 yd). Each gun featured a water cooled barrel and was fed using four-round clips. The gun's rate of fire was 120 to 160 rounds per minute and each gun was supplied with 2,000 rounds of ammunition. The 4.0 cm twin mounts were tri-axial stabilized fitted with electro-hydraulic power traverse and elevation and could train a full 360 degrees at a rate of 26 degrees per second and could elevate from -15 to +90 degrees at a rate of 24 degrees per second. The 2 cm (0.8 in) Flak L/70 gun was originally designed an aircraft cannon and fires a 130 g (4.586 oz) 20 mm high-explosive incendiary with tracer (HEI-T) projectile at a muzzle velocity of 880 meters per second (2,900 ft/s). The gun uses a gas delayed blowback operating mechanism with a cyclic rate of fire of 700-750 rounds/min and is fed using 60 round drum magazines. The 20mm guns were mounted in tri-axial stabilized quadruple mounts with electro-hydraulic training and elevation and could train a full 360 degrees at a rate of 30 degrees per second and could elevate from -15 to +90 degrees at a rate of 60 degrees per second. 2,000 rounds of ammunition was supplied for each 20mm gun.

Fire control

The fire of the main batteries was directed by three director towers, one each located above the forward and aft conning towers and one mounted above the foretop platform on the maoi mast. Each director tower was fitted with a 13.5 m (44.3 ft) meter stereoscopic rangefinder and an FMG 43/3 radar antenna. The FMG 43/3 radar antenna was 2.4 m (7.9 ft) wide by 0.6 m (2.0 ft) tall and operated at a 3 cm wavelength at a frequency of 10,000 MHz with peak power output of 50 kW. These radars had a rangefinding accuracy of 5 m (16.4 ft), bearing accuracy of 3 mils, and could track battleship sized targets out to 37,000 m (40,000 yd) and could discern 42 cm shell splashes out to 38,400 m (42,000 yd). Each director could operate in optical only mode with the stereoscopic rangefinder providing range and bearing, radar only mode with the FMG 43/3 radar providing range and bearing, or hybrid mode with the FMG 43/3 radar providing range data and the optical rangefinder providing bearing data. The director towers were connected using armored communications shafts to two plotting rooms located underneath the armor deck below the waterline. Each main battery turret was also equipped with its own 13.5 m (44.3 ft) meter stereoscopic rangefinder to allow each turret to fire under local control if all three director towers were knocked out.

The secondary armament was controlled by four triaxially stabilised director towers, two located on either side of the superstructure aft of the forward conning tower, one located behind the main mast, and one mounted behind the rear superfiring main turret. The main battery directors the secondary directors were connected using armored communications tubes to four plotting rooms located below the waterline underneath the armor deck. Each secondary director tower was fitted with a 4 m (13.1 ft) stereoscopic rangefinder and an FMG 44/33 radar antenna. The FMG 44/33 radar has a 1.8 m (5.9 ft) by 1.8 m (5.9 ft) rectangular antenna and operated at a 33 cm wavelength with a frequency of 900 MHz with a peak power output of 110 KW. These radars had a rangefinding accuracy of 18 m (59.1 ft), bearing accuracy of 3 mils, and could track bomber sized targets out to 41,000 m (45,000 yd) and surface ship targets out to 27,000 m (30,000 yd).

In addition to the primary and secondary directors the ships were equipped with a FMG 41/10 surface search radar and FMG 44/15 air search radar located on the main mast behind the foretop director tower. The FMG 41/10 was a navigation and surface search radar with a 1.2 m (3.9 ft) wide by 0.4 m (1.3 ft) tall rectangular antenna and operating with a 10 cm wavelength at a frequency of 3,000 MHz with peak power output of 70 KW. The radar could be set to rotate at 4, 8, or 12 rpm and could detect destroyer sized targets out to 30,000 m (33,000 yd), battleship sized targets out to 41,000 m (45,000 yd). The FMG 44/15 air search radar was designed for long range detection of air targets and had a 1.8 m (5.9 ft) by 1.8 m (5.9 ft) rectangular antenna and operating with a 150 cm wavelength at a frequency of 200 MHz with peak power output of 200 KW. The radar was designed to rotate at 4.5 rpm and could detect bomber size targets out to 190 km (120 mi) and fighter size targets out to 140 km (87 mi).

Armor

The main armor belt of the ships was 300 mm (11.8 in) thick face hardened cemented armor mounted on 25 mm (1.0 in) thick side plating and ran from just forward of the forward gun turret to just aft of the rear gun turret, covering 70% of the ship's waterline length. The belt extended from 3.3 m (10.8 ft) above the waterline to 1.7 m (5.6 ft) below the waterline and tapered to a thickness of 170 mm (6.7 in) at its lower edge. The belt was capped on either end by 220 mm (8.7 in) thick transverse bulkheads. Aft of the rear gun turret the belt was reduced to 220 mm (8.7 in) thick and extended back past the steering gear where it was capped by a 150 mm (5.9 in) thick transverse bulkhead. The front of the ship forward of the "A" gun turret the ship was not protected by belt armor with the exception of a 60 mm (2.4 in) thick splinter belt running from the forward transverse bulkhead to the bow of the ship. The main armor deck was located 1 meter above the design waterline and made from homogeneous armor steel 200 mm (7.9 in) thick in the center with outboard sloped sections 175 mm (6.9 in) thick inclined downward at about 20º from the horizontal which connected to the lower edge of the main armor belt under the waterline. Aft of the central citadel the deck armor was reduced to 120 mm (4.7 in) in the center and sloping sections which along with the rear extension of the belt armor created an armored raft designed to protect the steering gear. The upper weather deck was 20 mm (0.8 in) thick over the stern, increasing to 50 mm (2.0 in) thick over the central citadel, and then decreasing to 20 mm (0.8 in) over the bow. An additional battery deck was located in between the weather deck and the main armored deck which was was 12 mm (0.5 in) thick over the stern, 20 mm (0.8 in) thick over the central citadel, and decreasing 12 mm (0.5 in) thick over the bow.

The main battery turrets were designed to have 400 mm (15.7 in) thick face hardened cemented armor faces, 250 mm (9.8 in) thick homogeneous armor sides, 330 mm (13.0 in) thick homogeneous armor rears, and a 250 mm (9.8 in) thick homogeneous armor roof. The secondary battery turrets were protected by 100 mm (3.9 in) thick faces and 60 mm (2.4 in) thick sides, rears, and roofs. The barbettes were 400 mm (15.7 in) thick face hardened cemented armor and stepped down to 220 mm (8.7 in) thick below the upper belt armor. The forward conning tower had 350 mm (13.8 in) thick face hardened cemented armor sides and a 220 mm (8.7 in) thick homogeneous armor roof with an 85 cm (33.5 in) diameter communications shaft with 220 mm (8.7 in) thick face hardened cemented armor walls running down to the main armor deck. Above the forward conning tower was the forward director tower which had 200 mm (7.9 in) thick face hardened cemented armor sides and a 100 mm (3.9 in) thick homogeneous armor roof. The rear conning tower was significantly less protected with 150 mm (5.9 in) thick sides and a 50 mm (2.0 in) thick roof and with a 70 cm (27.6 in) diameter communications shaft with 50 mm (2.0 in) thick walls running down to the main armor deck. The aft director tower was mounted above the rear conning tower and had 100 mm (3.9 in) thick sides and a 50 mm (2.0 in) thick roof. The foretop command post, located on top of the main mast, had 60 mm (2.4 in) thick sides and a 20 mm (0.8 in) thick roof with the foretop director tower having 30 mm (1.2 in) thick sides and a 20 mm (0.8 in) thick roof.

The torpedo defense system of the ships consisted of an outer void compartment and three inner liquid loaded compartments and was designed with the capability to resist a 500 kg (1,100 lb) TNT charge. The outer void compartment was filled with only air and the inner three liquid compartments were fueled with water or fuel oil. The outer void space was designed to allow the gases from a torpedo warhead explosion to expand and dissipate while the inner liquid loaded compartments were designed to stop any splinters created by the torpedo warhead detonation. The outer void spaces could also be flooded to correct any lists while the inner liquid loaded spaces were filled with pumps to drain them in order to regain buoyancy lost by a torpedo hit. Inboard of the three liquid loaded spaces was 45 mm (1.8 in) longitudinal torpedo bulkhead which ran vertically from the armor deck down to the ships triple bottom. The distance between the hull sides and the torpedo bulkhead was 5.5 m (18.0 ft) in the center of the ship, narrowing to 3.25 m (10.7 ft) on either sides of the gun turrets where the torpedo bulkhead thickness was increased to 60 mm (2.4 in) to compensate for the reduced depth of the torpedo defense system. The torpedo bulkhead also continued above the main armor deck as a 30 mm (1.2 in) thick longitudinal splinter bulkhead running up to the weather deck. The ships also featured a triple bottom 2.4 m (7.9 ft) deep along the bottom of the armored citadel with a 1.2 m (3.9 ft) liquid loaded bottom layer and a 1.2 m (3.9 ft) air filled top layer designed to provide protection against mines and under-keel torpedo explosions.