From an Post-WWII Report
There was nothing sensational about the design of Tirpitz; she was merely a very large battleship, designed on conventional lines, propelled by three screws driven by steam turbines and mounting eight 38 cm. (approx. 15-in.) guns in twin turrets, arranged in the conventional way, two forward and two aft. This German mastodon was designed to a standard displacement of 42,600 tons, although the displacement reported for Treaty conditions was 35,000, the same as that of the King George V and Washington classes of battleship, which were genuinely designed to this size. In the deep condition she displaced 50,000 tons and had a draught of nearly 34 ft. Other things being equal this greater displacement would have been accompanied by greater ability to withstand damage. Although she measured 822 ft. overall, her most impressive dimension was her beam of 118 ft. which would have prevented her from passing through the Panama Canal. It was always thought that this implied a very deep “bulge” for protection against underwater attack, but it is now known that there was nothing remarkable about her underwater protection which was, in fact, inferior to that fitted in both British and American contemporary Capital Ships. The very large beam was adopted to provide an abnormally high initial stability. Such measures, however, may often reduce the resistance of the ship to the more severe states of damage. It is doubtful whether Tirpitz was at all better than her allied counterparts in this respect.
Information gained from a survey of the wreck and numerous drawings brought from Germany confirm that Tirpitz’s reputed fine watertight subdivision, and consequent “invincibility”, were a complete myth; her subdivision was very similar to that of our own Capital Ships, and indeed those of all major sea Powers. Her watertight integrity was in several ways subordinated to requirements of convenience; for example, every transverse watertight bulkhead in the ship was pierced by watertight doors on the lower and middle platform decks, a menace which has been eliminated from H.M. ships for many years, and the engine rooms seemed to contain far more space than was needed.
Some of the available weight was used to secure a very high speed. Tirpitz was designed to develop 150,000 shaft horse-power which enabled her to make over 30 knots in the average action condition, and she was capable of developing 165,000 shaft horse-power for sudden bursts of over 31 knots. Her range based on an oil fuel capacity of 5,000 tons was over 10,000 sea miles. More fuel could be carried in an emergency.
More of the extra displacement in Tirpitz was accounted for by the fact that her 38 cm. guns were mounted in twin turrets rather than the weight saving triple and quadruple arrangements used in modern American and British Capital ships. Also the Germans fitted separate low angle and high angle secondary batteries rather than the dual purpose mountings used in Allied ships. She thus had twelve 15 cm. (5.9-in.) low angle guns in twin turrets, three on either side of the amidships superstructure, and sixteen high angle 10.5 cm. (4.1-in.) guns in twin mountings – four on each side. A further battery of sixteen 3.7 cm. (1.46-in.) mountings for close range anti- aircraft work was also provided.
This powerful armament was controlled by range-finders and director sights on the forward and after conning towers, and on the fore top. There were smaller range-finders for the secondary armament, one on each side of the bridge. The 10.5 cm. H.A. armament was controlled by four special gyro stabilized directors, one to port and one to starboard of the bridge, and two on the centre line abaft the main mast.
Tirpitz’s general layout is illustrated by the small-scale drawing (Figure 2) which has been prepared for this report from larger scale drawings found in the Naval Arsenal at Kiel. It will be seen from the drawing that the machinery spaces, consisting of six boiler rooms, three engine rooms and miscellaneous compartments housing auxiliary machinery, the magazines and shell rooms, and other vital compartments such as fire control rooms, were well protected by a long armoured citadel. The sides were of 320 mm. (12.6-in.) thick cemented armour plates from 8 ft. below the waterline up to the battery deck and thinner plating of 145 mm. (5.7-in.) thickness to the upper deck. In addition, the third deck down was armoured with 80 mm. (3.15-in.) non-cemented plating over the machinery spaces and 100 mm. (3.94-in.) over the magazines between the torpedo bulkheads, while the sloping deck armour between the centre portion and the base of the side armour was 110 mm. (4.33-in.) in way of machinery spaces and 120 mm. (4.72)-in.) in way of magazines. There were extensions of the citadel by thinner armour, the lower belt being 60 mm. (2.36-in.) plating forward and 80 mm. (3.15-in.) aft and the upper belt being 35 mm. (1.38-in.) forward and aft. While there was no deck armour before the forward magazines, deck protection aft over the steering gear compartments was 110 mm. (4.33-in.) in thickness. This armoured citadel, re-inforced by a strength deck (the upper deck) which was 50 mm. (1.97-in.) thick generally, afforded efficient protection against splinters and all but the largest bombs dropped from a considerable height. Barbettes, and turret sides and roofs, and conning towers were protected by armour on the same generous lines.
Four sea-planes which were carried for spotting and reconnaissance were accommodated in special hangars abreast the funnel and under the main mast. They were launched by a fixed athwartships catapult between the funnel and the main mast.
Attack by Fleet Air Arm Torpedo Bombers
On 6 March, 1942, H.M. Submarine Sealion, on patrol off the northern entrance to Trondheim, reported an enemy heavy ship proceeding on a north-easterly course. As a convoy on passage from Iceland to North Russia had been shadowed by a Focke-Wulf aircraft on the previous day, it was thought possible that the battleship Tirpitz might have left Trondheim to attack it. The C.-in-C., Home Fleet, in the King George V, with the Duke of York, Renown and Victorious, were at sea covering the convoy. On the following day C.–in-C., Home Fleet, intercepted a distress message from the Russian Ijora in position 72° 35’ N, 10° 50’ E. Early on 9 March six Albacores were flown off Victorious to search the area in which Tirpitz was believed to be operating. She was sighted at 0800 and a striking force of 12 Albacores armed with torpedoes, which had been flown off Victorious at 0735, was guided to the target by the shadowing aircraft. At 0842 Tirpitz was sighted by the torpedo planes which attacked in two waves, one on each side of the ship. The torpedoes appear to have been dropped at an excessively long range which enabled Tirpitz to “comb the tracks”, turning sharply first to port and then to starboard. No hits were scored, but the German command seemed to have been somewhat scared because Tirpitz retired at high speed to her safe anchorage in the Foetten Fjord near Trondheim.
Early Bomber Command Attacks
In the Foetten Fjord she was immune from most forms of attack; she lay surrounded by mountains and was moored close in to the cliffs on one side and surrounded by torpedo nets on all others. On the occasional fine day which made air attack just possible she had only to put up a smoke screen to rectify the climatic defect. Despite these difficulties she was attacked by Bomber Command aircraft during the early hours of 31 March, and 28 and 29 April, 1942. The weather conditions during the first of these attacks were so bad that only one aircraft succeeded in finding Tirpitz at all, the usual smoke screen was in use and the attack was abortive. During the second and third attacks, most of the aircraft despatched, 32 and 30 respectively, managed to find the ship but again the smoke screen prevented useful results from being achieved. The Germans who were interrogated after the surrender reported that in one of these attacks the bombs (probably hydrostatically fused mines) rolled down the cliff into the sea – a mode of attack which they regarded as worthy of more success than it achieved.
Although the difficulties of carrying out an attack against a Capital Ship under these conditions are fully appreciated, the 4,000 lb. blast bombs with instantaneous fuses which seem to have constituted the major part of the bomb loads carried in these early attacks, were rather unsuitable. A hit would have caused only superficial damage to superstructures, while near misses would have detonated on the surface with little fragmentation and practically no effect on such a heavy ship. 2,000 lb. A.P. bombs dropped in level flight would have been a better choice, since twice as many of these bombs could have been carried and any hits would have had a direct effect on the vessel’s fighting efficiency. The small Mk.XIX mines containing 100 lbs. of explosive and fitted with hydrostatic fuses to operate at 30 ft. depth had an almost negligible target, and the 500 lb. and 250 lb. G.P. bombs had little chance of producing serious damage against a ship of this size.
Tirpitz had a very quiet time from April, 1942, until March, 1943, during which period nothing useful was accomplished. At the end of this period Scharnhorst and Lutzow joined forces with her in the Altenfjord; these three ships with their attendant destroyers constituted a serious menace to the Russian convoys, which were suspended during the long daylight of the summer months for this reason. In early September, 1943, the squadron made a raid on Spitzbergen, showing that it was beginning to feel somewhat more aggressive, then returned to the anchorages in various branches of the Altenfjord. Tirpitz lay moored in Kaa Fjord – an arm of the Altenfjord some fifty miles from the sea – completely protected by torpedo nets. Though he disposed a superior Naval Force, it was extremely difficult for the C.-in-C., Home Fleet, to tempt the three ships to action from over 1,000 miles away, or to lay on a successful air or submarine attack against such secluded foxholes. It was finally decided to attack them with the new midget submarines officially known as X-Craft, which each carried two special ground mines, and which had been evolved after a careful study of the specific problem of attacking enemy units in such anchorages.
Six of these novel craft (X5 to X10) which had recently joined the Fleet, set out on the night of 11/12 September, 1943, on the hazardous journey to a position off the Norwegian coast, towed by ‘S’ and ‘T’ Class submarines. Two of them, X8 and X9, failed to complete this passage but the remaining four reached their rendezvous on 20 September, slipped their tows and proceeded independently to the attack.
X10’s periscope and compasses immediately began giving much trouble and eventually failed completely; as a result, she had to retire from the attack. (The plan had been for X5, X6 and X7 to attack Tirpitz, X8 to attack Lutzow and X9 and X10 to attack Scharnhorst). During 20, 21 and 22 September, X5, X6 and X7 successfully negotiated the Altenfjord as far as the anchorage of Tirpitz in Kaa Fjord, passing en route mine fields, enemy surface vessels and the anti-submarine boom defence at the entrance to the Kaa Fjord.
X6 entered the torpedo net enclosure around Tirpitz at about 0705
G.M.T. using the official entrance which was open at the time for the passage of store ships (see Figure 3). After a series of instrumental defects had caused her to surface three times (she was mistaken for a porpoise on the first occasion, correctly identified on the second (at 0710) and attacked with machine-gun fire and hand grenades on the third), X6 succeeded in releasing her two charges under the ship abreast ‘B’ turret. As escape was then impossible, she was scuttled and her crew surrendered. Meanwhile, X7 endeavoured to penetrate the net defence by passing under it. She experienced a number of setbacks but eventually succeeded in entering the anchorage. Passing down it under the keel of Tirpitz, from forward to aft, she released one charge abreast ‘B’ turret and the other further aft, under the after Engine Room. This X-Craft left the enclosure at 0740, this time sliding over the nets, and then dived. During the manoeuvre she was sighted by the Germans and hit several times with machine-gun bullets. At 0812, while still submerged, the crew heard a tremendous explosion which they thought to be due to the explosion of the X-Craft charges. X7 subsequently became uncontrolled; it was decided to scuttle her and at 0835 she was brought to the surface, but sank again with her hatch open after only one member of the crew had managed to escape. The full movements of X5 are not known but she was seen at 0835 on the surface some 500 yards outside the nets, when she was fired upon by Tirpitz and appeared to sink.
There were thus four charges laid under or near Tirpitz, namely, one placed by X7 under the after engine room and three from X6 and X7 abreast ‘B’ turret.
From the German point of view, the first intimation that an attack was in progress came at about 0713 when a small craft (X6) – correctly identified as a submarine – was observed to break surface momentarily inside the torpedo nets about 200 to 250 ft. off the port beam. The submarine alarm was sounded, watertight doors were brought to the action state and the anti- aircraft guns were manned. The submarine was sighted again at 0720 and was attacked with 20 mm. and 37 mm. fire from Tirpitz and hand grenades thrown from a motor boat which had been despatched to attack her. The X-Craft was eventually brought to the surface and abandoned in a sinking condition by her crew. The motor boat tried to tow the submarine, which the Germans suspected might contain explosives, away from the battleship but it sank at 0732, some 50 to 60 yards off the port bow.
The Germans were aware of the existence of British midget submarines but had no information as to their armament. They were, therefore, undecided as to whether an attack by torpedoes, mines, or limpet charges had been made. To clear any limpets which might have been attached to the bottom, they pulled from stem to stern a wire strop slung around the ship under the keel. At the same time, preparations were made to get underway but, in view of the unknown menaces awaiting the ship in the fjord, it was ultimately decided to remain inside the nets. However, Tirpitz’s bow was moved away from the submarine known to have sunk off the port bow by tightening and slackening the port and starboard forward mooring cables. Unbeknown to the Germans this had the effect of clearing the forward part of the ship from the three charges placed abreast ‘B’ turret. The single charge aft remained effective.
Shortly after this evolution was complete at least two heavy explosions occurred in quick succession; spray was thrown up over the ship which shuddered violently. The other two X-Craft were destroyed in turn soon after this. An intensive depth charging of the fjord followed.
Although only one of the six charges originally intended for Tirpitz was effective, the results were undoubtedly worthwhile. Only a relatively small quantity of water entered the ship but damage to main machinery was enough to immobilize her for six months. It is doubtful whether the repairs carried out in Kaa Fjord restored the ship to her original standard of mechanical efficiency.