JR Potts, AUS 173d AB (Updated: 9/30/2013):
The KMS Tirpitz Joins the KMS Bismarck
When completed, Tirpitz was the largest and final battleship to be built by the Germans - even longer and heavier than the well-known KMS Bismarck. Discussions surrounding her design included an increase to overall displacement to 37,200 tons. However, Admiral Erich Johann Albert Raeder (1876-1960) instructed the designers not to exceed the original 35,000-ton design as the hull size needed to conform to existing locks as well as comply with the available harbor depths at the German dock facilities. The Kriegsmarine Planning Office felt the ship's design could not be reduced below a 37,200 ton range due to the normal construction methods that always seemed to increase the weight of any ship being built. Reluctantly, Raeder agreed to the extra tonnage but this being allocated to weapons. Meanwhile, the Construction Office was investigating four different main propulsion arrangements to power the Tirpitz. They were as follows: 1) High pressure steam geared turbines with 12 x boilers in 6 x boiler rooms forward of the turbine rooms, 2) Same as (1) but with all 12 x boilers in 3 x boiler rooms forward of the turbine rooms, 3) Same as (2) but with one boiler between the forward turbine rooms and 4) a Turbo-electric drive.
The Construction Office decided that (2) was the best propulsion arrangement for the new vessel. There were some in the ranks that wanted (4) but the excessive weight of the turbo drive was a major concern to the design. A conference was held on June 6th, 1935 to review the ships secondary armament and, once again, the design team brought up the main propulsion discussion. New encouraging results concerning the turbo-electric drive were brought to Admiral Raeder's attention. The machinery, being built by Lloyd Liner Scharnhorst, had reopened the consideration of this propulsion method even though the turbo drive weighed 600-tons more than the conventional geared turbines to be used. The German Navy Construction Office still had reservations about the turbo-electric drive weight and considered housing the secondary guns in casements instead of turrets to save on tonnage. Raeder disagreed that protection should be sacrificed around the secondary guns and instructed the Planning Office to look elsewhere and save the required weight before the intriguing turbo-electric drive would be considered.
The Construction Office provided Raeder with a new plan in August of 1935 designated as "A13". The report outlined improvements and included a sketch of a three-shaft, turbo-electric drive. Raeder reviewed the plan and agreed to allow the changes to be made to his Tirpitz. This decision created a lot of planning concerns related to armor thickness, the reduction of the citadel length and even the positioning of living spaces within the hull. By June of 1936, difficulties in the weight reduction phase forced the Planning Department into the decision that the turbo-electric drive installation should be cancelled and geared turbines be adopted for Germany's battleship instead.
Of course Raeder felt much time had been lost by the Planning Department's indecision to this point and now the construction drawings would have to be redone. With conventional turbines being adopted, Raeder took the opportunity to reverse the initial reduction of the main armor belt from 300mm back up to 320mm thickness. Additional savings in weight changes were made using welded armor decking instead of rivets and this allowed for armor increases above the main magazines - increasing from 95mm to 100mm - and slopped areas from 110mm to 120mm. By 1936, armor thickness could not be changed because rolled armor construction had begun on the ship. The belt was 145mm (5.709 in) to a maximum of 320mm (12.598 in). The decks ranged from 50mm (1.569 in) to 120mm (4,724 in) and Bulk heads were a consistent 220mm (8.661 in). The anti-aircraft barbettes - a compilation of 16 x 30mm AA guns, 16 x 37mm AA guns, 92 x 20mm AA guns - were protected by 342mm (13.465-inches). All secondary 12 x 5.9 inch guns had 130mm (5.709 in) and the main 8 x 15 inch gun turrets were given 360mm (14.173 in) armor. After the superstructure and armaments were added, Tirpitz would displace 53,500-tons loaded and had an overall running length of 832 feet. Her maximum speed was 30.8 knots and she had a range of 8,870 nautical miles at 19 knots.
Installed were two quadruple banks of 21-inch torpedo tubes on the main deck just aft of the aircraft launch catapults. The ship was fitted for up to six floatplane aircraft used for spotting "over-the-horizon" targets of opportunity and enemy scouts. These aircraft were launched via 1 x fixed, double-ended catapults fitted amidships, the aircraft being recovered by crane after landing alongside the vessel by their integral floats. Abreast of the funnel were two single hangers while under the mainmast was a larger hanger. The ship could support four to six Arado Ar 196 floatplane aircraft as needed.
The finalized main steam plant was comprised of 12 x 2 pairs of boilers in six boiler rooms fitted fore and aft. The boilers were built by Blohm & Voss at Deschimag for Tirpitz (Blohm und Voss would also become known throughout the war for their many large flying boat designs). The geared turbine installation was a three-shaft layout with the center turbine room furthest aft and the side turbines in separate compartments aft of the boiler rooms. Normal full power rating was 265rpm per shaft providing 38,300 shaft horsepower with 46,000 shaft horsepower at maximum power. Electric power was supplied by four main generator rooms on the lower platform deck. Number 1 was starboard and Number 2 was on the port side with each housing four generator sets of 500kW. Number 3 and 4 generator spaces were similarly arraigned with three 690kW turbo generators each. Oil bunkerage capacity for Tirpitz was 8,297 tons but only 7,780 tons were able to be pumped. Endurance figures were estimated at 8,600nm @15kts, 8,150nm @ 21kts, and 3,750nm @ 30kts. However, wartime figures could not be estimated due to unknown - and ever changing - factors.
The 380mm SKC/34 main guns were a new design of the Krupp Company, weighing 112kg, and fired an 800kg projectile. The Tirpitz carried 130 projectiles per gun. Munitions carried onboard for the other guns varied. The design plan called for 12 x 105 rounds for the 150mm, 16 x 400 rounds for the 37mm cannons and 16 x 2,000 rounds for the 37mm.