Aegir-class Battleship

Aegir class

Aegir class battleship in 1940
Class overview
Name:	Aegir class
Builders:	Isenstadt Naval Works
Operators:	Arcaenian Königsmarine
Built:	1918–1924
Planned:	4
Completed:	4
General characteristics (as built)
Type:	Fast battleship
Displacement:	43,800 t (43,100 long tons) (normal) 53,600 t (52,800 long tons) (full load)
Length:	270 m
Beam:	33.5 m
Draft:	10.0 m standard 10.6 m full load
Installed power:	160,000 shp (120,000 kW) 24x oil-fired water tube boilers
Propulsion:	4x steam turbines 4x shafts
Speed:	30 knots
Range:	8,000 nautical miles (15,000 km) at 16 knots (30 km/h)
Complement:	1,300
Armament:	8 × 42 cm (16.5 in) SK L/45 guns 8 × 15.0 cm (5.9 in) SK L/45 guns 4 × 15.0 cm (5.9 in) FlaK L/45 guns 3x 70 cm torpedo tubes
Armor:	Main belt: 350 mm (13.8 in) Upper belt: 250 mm (9.8 in) Bulkheads: 250 mm (9.8 in) Barbettes: 350 mm (14 in) Turret face: 350 mm (14 in) Conning tower: 350 mm (13.8 in) Decks: 60–120 mm (2.4–4.7 in)

Design

General characteristics

The Aegir-class battleships had an overall length of 270 meters, a beam of 33.5 meters, and a draft of 10.6 meters at full load. They displaced 43,800 tonnes at normal load and 53,600 tonnes at deep load. Externally the ships were similar to the Königsmarine's preceding Heimdall-class Battlecruisers and were built with a single tripod foremast mounted atop the large forward superstructure and a lighter pole main mast aft of the rear funnel. The hull was constructed from longitudinal steel frames made of mild steel with riveted on outer hull plates and was divided longitudinally into 21 watertight compartments and featured a double bottom running for 90 percent of the length of the hull. The ships featured a flush upper deck with a high freeboard and were fitted with a bulbous bow to reduce drag on the hull. Despite their longer length the ship's had a metacentric height of 2.5 m at full load, making them very stable gun platforms with a gentle, predictive rolling motion.

Propulsion

The Aegir-class ships were equipped with four sets of steam turbines each of which drove a propeller shaft with a 4.5 meter diameter three-bladed propeller .The starboard propellers rotated to the right, and the port propellers to the left. Each turbine was rated at 40,000 shp (30,000 kW) at 1,360 RPM and drove a propeller shaft through a Föttinger type hydraulic gear reduction unit with a 4.3 to 1 reduction ratio and a 90% mechanical efficiency. The machinery was divided into eight compartments, one for each turbine unit and one for each condenser and auxiliary machinery for each turbine. Steam for the turbines was provided by 24 oil-fired double-ended boilers working at a pressure of 1,620 kPa (17 kgf/cm2) with exhausts trunked into a pair of large funnels. The powerplant was rated at 160,000 shp (120,000 kW) at 315 shaft revolutions per minute which gave the ships a maximum speed of 30 knots. Standard bunkerage was 4,000 tonnes of fuel oil which gave the ships a range of 8,000 nautical miles (15,000 km) at a cruising speed of 16 knots (30 km/h). Electrical power on the ships was provided by six 750 kW DC diesel generators that provided a combined 4,500 kilowatts at 220 volts. Two additional auxiliary DC diesel generators were also installed as backups. Each generator set included a 1,000 PS diesel engine driving a 750 kW dynamo connected to an electrical distribution board. The ship's electrical circuit was divided into four zones; bow, stern, port, and starboard, each of which could be powered by any of the ship's generators. Electrical power for AC devices including the steering indicator and engine telegraphs was provided by four 50V alternating current generators with an additional two DC-AC converters for the ship's radio room.

Auxiliary machinery

Like other Arcaenian ships the Aegir-class ships were equipped with a drainage and pumping system that could drain any compartment of the ship. The drainage system was divided into eight independent groups which were connected using 35 cm diameter drain pipes running along either side of the ship along with 12 and 14 cm diameter auxiliary drainage pipes connecting each compartment. The ships central pumping room contained four steam driven and two electrical driven high-capacity centrifugal pumps. The pumps for the ship's condensers could also be connected to the draining system to pump out water faster. As a backup the ship was also equipped with four portable electric pumps and four portable hand pumps. Flooding of side compartments to correct lists was provided by a set of hydraulically opened kingston valves controlled from a central flooding control station which could correct a 5 degree list in 15 minutes. Each kingston valve could also be manually opened. Flooding of the magazines was accomplished using an additional set of kingston valves with a maximum flow rate o 3600 tonnes/hour which could completely flood the propellant magazines in 4 to 5 minutes. A refrigeration system was provided for the ship's propellant magazines and food storerooms. Two desalination plants on board were designed to produce a total of 600 tonnes of fresh water per day for feed water, drinking and washing water.

Steering gear

Steering was accomplished by twin rudders each with a 24 meter surface area mounted behind each of the inner propeller shafts installed at a 6 degree angle relative to the centerline. The rudders were powered by two three-cylinder steam engines through a spindle screw drive with the rudders being mechanically coupled so that each engine could drive both rudders or each rudder individually. Each rudder also had a backup manual drive with three hand wheels. Maximum rudder deflection for each rudder was 45 degrees. Minimum turning radius for the ships was determined to be 900 meters at a speed of 21 knots.

Armament

Main battery

The primary armament of the Aegir-class battleships consisted of four 42 cm SK L/45 guns mounted in four two-gun turrets in two superfiring pairs along the centerline, one pair forward and one pair aft with the aft turrets separated by the ship's engine rooms. The guns were designed to fire 1,030 kg (2,270 lb) kg projectiles at a muzzle velocity of 810 meters per second (2,700 ft/s) out to a maximum range of 36,400 m (39,800 yd) at an elevation of 30 degrees. The Psgr. L/3.5 armor piercing shell had a length of 3.5 calibers and was fitted with a hard armor peircing cap and an aluminum ballistic cap with a 4 caliber-radius-head (CRH) ogive and contained a 30 kilogram TNT bursting charge. The Spgr. L/4.1 high explosive shell had a length of 4.1 calibers and contained a 90 kilogram TNT bursting charge and was fitted with a base mounted fuze that would detonate 3 to 6 meters behind the point of impact when impacting unarmored or lightly armored parts of a ship. Armor peircing shells were painted blue while high explosive shells were painted yellow. Total ammunition stowage was 720 rounds or 90 rounds per gun with the typical shell allotment being 60 AP rounds and 30 HE rounds per gun. Rate of fire was around 2-2.5 rounds per minute per gun. The guns used a horizontal sliding wedge breech block with the propellant charge consisted of a 135 kg (298 lb) fore charge contained in a silk bag and a 128 kg (282 lb) main charge contained in a 90 kg (200 lb) brass case which acted to seal the breech.

The gun turrets were trained and loaded with electric motors with elevation and shell hoists being hydraulically powered. The forward two turrets were capable of traversing +150 / -150 degrees and the rear two turrets +155 / -155 degrees from centerline at a speed of 3 degrees per second and elevating from -5 to +30 degrees at a speed of 5 degrees per second. Traversing gear for each turret consisted of a 120 kW electric main motor along with an auxiliary electric motor capable of traversing each turret at a rate of 0.5 degrees per second. The turret itself rotated on a ball race with 200 ball bearings with a diameter of 16.5 cm. Elevating gear consisted of a hydraulic cylinder for each gun with a backup manual elevation drive. Hydraulic power for each turret was provided by two three-cylinder hydraulic pumps each driven by a 150 kW electric motor. Backup electrical power to each turret was also provided by a pair of 90 kW generators. The turrets each had a machinery room below the turret with a handling room for shells and fore charges beneath it. Magazines for the rear and additional fore propellant charges were located underneath the handing rooms. Projectiles were transferred from the handling room to the turrets using hydraulically powered hoists. Once in the turret the shells and cartridges were electrically rammed to the rear of the turret onto pairs of electrically powered loading cars running on a set of rails which transferred the shells and cartridges to each gun. The shells and cartridges were then rammed into the guns using an electrically powered chain and a hydraulically powered telescoping rammer, the shells and fore charges rammed first followed by the cartridge case with the main propellant charge. Loading the guns required them to be returned to 2.5 degrees elevation. The control position for each turret was located at the rear of the turret and controlled the elevators, munition cars, and rammers and had a good overview of the entire loading operation. Smoke extraction from turret was done by two independent electric motor powered fans connected to a common suction line which exhausted through a port located on the underside of the turret underneath the control position which was protected against splinters by an armored grating.

Secondary battery

The secondary battery of the ships consisted of eight 15 cm (5.9 in) SK L/45 guns mounted in armored casemates mounted along the sides main deck grouped around the fore and aft main battery turrets and were intended for defense against destroyers and torpedo boats. The guns fired 45.3 kg (100 lb) shells at a muzzle velocity of 835 meters per second (2,740 ft/s) and were loaded with a 13.7 kg (30 lb) RPC propellant charge contained in a brass case. Each casemate had its own magazines and ammunition hoists which could supply up to 7 complete rounds per gun per minute. Each gun could depress to −7 degrees and elevate to 30 degrees with a maximum range of 17,600 m (19,200 yd) at 30 degrees elevation. Each ship was supplied with 1,280 rounds of 15 cm ammunition with 160 rounds per gun.

Anti-aircraft battery

The anti-aircraft armament of the ships consisted of four 15 cm (5.9) in FlaK L/45 guns mounted in enclosed pedestal mounts grouped around the rear superfiring main battery turret. These guns were the same as the 15 cm (5.9 in) SK L/45 guns but mounted in high angle mountings which allowed depression to −10 degrees and elevation to 70 degrees. The guns had a maximum range against surface targets of 18,400 m (20,100 yd) at 45 degrees elevation and a maximum AA ceiling of 10,400 m (11,400 yd) at 70 degrees elevation. The guns could also fire 41.0 kg (90.4 lb) illumination rounds. Each gun was supplied with its own magazine and ammunition hoists with a rate of fire was around 5-7 rounds per minute with each gun being supplied with 200 rounds of ammunition.

Torpedo armament

As was typical for capital ships of the era the ships were armed with submerged torpedo tubes with one 70 cm (27.6") tube in the bow and two tubes on either beam to the rear of the engine rooms supplied with a total of 15 torpedoes. The torpedoes were the J9 type which were 9 m (30 ft) long and carried a 315 kg (694 lb) Hexanite warhead. The torpedoes used a decahydronaphthalene (decalin) wet-heater propulsion system and had a range of 18,000 m (20,000 yd) at a speed of 30 knots or 10,000 m (11,000 yd) at a speed of 36 knots.

Searchlights

As originally the built the ships were fitted with a total of eight 110cm searchlights rated at 150 amperes: four mounted on a forward searchlight bridge around the foremast and four on an aft searchlight bridge mounted around the aft mast. The searchlights were controlled remotely from two independent control positions, one in each conning tower. Two 17-ampere signal searchlights were also carried on the bridge.

Fire control

The main and secondary battery of the Aegir-class battleships was controlled from four fire control posts, one fire control director in the forward conning tower, another fire control director in the aft conning tower, an observation post located atop the main mast, and another observation post atop the aft mast. Each fire control position was fitted with an 8.0 meter base coincidence rangefinder with 15x and 30x magnification which replaced the 5.0 meter base rangefinders used on previous Arcaenian ships and was designed to give accurate range measurements at distances up to 30 kilometers in order to match the performance of the larger 42 cm guns. Each turret was also equipped with a 10.5 meter base coincidence rangefinder for local control. The forward fire control director occupied the rear portion of the forward conning tower and was staffed by a total of 23 men. The main platform including a senior artillery officer, an artillery officer controlling the medium 15 cm battery, two rangefinder operators, two midshipman, three non-commissioned officers, and five communication operators. Below the main platform sat an additional six signalmen and below them sat a reserve non-commissioned officer, a non-commissioned officer electrical engineer, and two additional communications operator sailors. The conning tower was fitted with viewing ports covered by armored doors with vision in battle provided by a set of periscopes. The director post was fitted with four "Richtungsweiser" optical target designators with an 8x to 24x times magnification (Field of view: 6.25 ° - 2 °), two on each side of the conning tower, that allowed the artillery fire control officers to direct the ship’s main and secondary battery as well as rangefinders and spotters onto the chosen target. The optical target designators electromechanically transmitted the bearing values of tracked targets to every gun, rangefinder and searchlight position on the ship, allowing the gunners and other rangefinder and searchlight operators to rotate the turret, rangefinders, and searchlights onto designated targets. The aft director post was arranged similarly to the forward director and was commanded by a second senior artillery officer. The two observation posts located atop the main and aft masts each housed an observer officer, a signalman, and an artilleryman who transmitting information about the fall of shells along with a non-commissioned officer observer of medium-caliber artillery and two signalman sailors.

Data from the rangefinders was fed into one of two below deck plotting rooms, one for the 42 cm guns and one for the 15 cm guns which received all fire control commands from the fire control posts via telephones and speaking tubes with fire control instruments in the plotting rooms which then transmitted firing commands to the guns. Each fire control post was equipped with an electro-mechanical range-averaging device (Mittlungs Apparat or M.A. )which automatically and continuously calculated a mean rangefinder range which drastically increased the accuracy of the calculated rangefinder ranges by averaging out the error from each rangefinder. When any of the ship's range-finder operator would make a range estimate, his assistant on the range-finder position would immediately enter and electrically transmit the value to the M.A. Whenever a new reading was received from any of the range-finders, the M.A. would automatically generate an averaged value of all the latest readings of each range-finder position which would then be compared to the estimated range value generated by the range clock . If the values differed, the speed of the range clock could be adjusted by means of a lever until the range clock value matched the averaged range-finder value of the M.A. Range values from the range-clock as well as the range-rate and deflection based on target heading, bearing, and speed would then be automatically transmitted to the sight-setter positions at each gun turret.

During combat the guns were targeted using rangefinder data and the firing was intended to be carried out in half salvoes alternating between the forward and rear turrets. Adjustments to the fire was then carried out by observing the fall of the shells and making range corrections. To distinguish the splash of the ships own shells an elctrical timer was installed in all four fire control posts which was turned on whenever the guns were fired and after a 10-60 second delay (depending on the range to the target and the calculated flight time of the shells) would transmit a beating sound in the headphones worn by the senior artilleryman in each fire control post.

Armor

The main armor belt of the ships was 350 mm (13.8 in) thick and ran from slightly forward of the forward main battery barbette to slightly aft of the rear main battery barbette which protected the central citadel of the ship containing the ammunition magazines and the machinery spaces. The main strake extended from 195 cm (76.8 in) above above the waterline to 35 cm (13.8 in) below the waterline where it tapered to a thickness of 170 mm (6.7 in) along its lower edge. Directly above the main belt armor was a 250 mm (9.8 in) thick strake of armor plating extending up to the main deck which covered the sides of the hull above the main belt. Forward of the forward turret the belt armor was stepped down to 200 mm (7.9 in) and then to 150 mm (5.9 in) tapering down to 130 mm (5.1 in) at its lower edge with a 30 mm (1.2 in) thick splinter bulkhead extending from the forward edge of the belt all the way to the bow. Aft of the rear gun turret the belt stepped down to 200 mm (7.9 in) tapering down to 150 mm (5.9 in) at its lower edge which extended all the way back to the stern and protected the ships steering gear.

The main armor deck was 60 mm (2.4 in) thick over the central citadel with 100 mm (3.9 in) thick sloped sections on either side of the main armor deck extending down at a 30 degree angle to meet the lower edge of the belt armor. This formed a classic "turtle deck" armor scheme where shells fired by enemy warships would have to penetrate both the 350 mm (13.8 in) thick main belt and the 100 mm (3.9 in) thick sloping deck armor to penetrate into the ships vitals and was designed to provide immunity against 1,000 kg (2,200 lb) 16 in (406 mm) shells fired at any range over 11,000 m (12,000 yd). Aft of the central citadel the thickness of the armor deck increased to 100 mm (3.9 in) with 120 mm (4.7 in) slopes which along with the aft extension of the main belt armor formed an armored raft designed to protect the steering gear of the ships. Above the main armor deck was the forecastle deck which was 20 mm (0.8 in) thick aft, increased to 40 mm (1.6 in) in the central part of the ship, and decreased down to 20 mm (0.8 in) thick over the bow. An additional a 30 mm (1.2 in) thick longitudinal splinter bulkhead extended from inboard edges of the sloped part of the armor deck up to the forecastle deck.

The main battery turrets had 350 mm (13.8 in) thick faces, 250 mm (9.8 in) thick sides, and 290 mm (11.4 in) thick rears to balance them while the turret roofs were 150 mm (5.9 in) thick. The main battery turret barbettes were 350 mm (13.8 in thick on the front and sides and 250 mm 250 mm (9.8 in) on the rear. Below the upper belt armor the barbette thickness was reduced to 150 mm (5.9 in) and then to 100 mm (3.9 in) below the main belt armor. The 15 cm casemate guns had 170 mm (6.7 in) thick armor plating for the casemates while the guns themselves had 80 mm (3.1 in) thick shields to protect the crews from shell splinters. The 15 cm (5.9 in) FlaK guns were enclosed with 20 mm (0.8 in) thick gun shields to protect their crews from splinters. The forward conning tower had 350 mm (13.8 in) thick sides and a 170 mm (6.7 in) thick roof while the aft conning tower had 250 mm (9.8 in) thick sides and an 80 mm (3.1 in) thick roof.

The underwater protection of the ships was designed to withstand a 300 kg (660 pound) hexanite charge and consisted of an outer air space, an 8 mm (0.31 in) thick bulkhead, an inner liquid loaded layer, and a 60 mm (2.4 in) thick torpedo bulkhead located 3-5 meters inboard from the side of the ship which ran the length of the hull and extended from where the inboard edges of the sloped part of the armor deck down to the ship's double bottom. The inner liquid loaded layers were filled with water as fuel oil was burned and were fitted with compressed air systems which could rapidly blow the liquid out of the buoyancy spaces and restore the ships buoyancy in the event of a torpedo hit or flooding.