Th e Underwater Explosion Test

the lack of vertical armor over the main belt. Based on their calculations they stated that a heavy projectile arriving at an angle of 7 degrees or more could slip above the main belt and easily penetrate the 30 mm thick Mitteldeck and the 36 mm thick armored deck one level below and reach the magazine (cartridge room). On the 24,500 ton design, unlike on the Tegetthoffs, the 35 cm magazines were directly below the armored deck and their upper parts were above the waterline.370 Th e Arsenal proposed thickening the Mitteldeck over the magazines of the triple turrets to 50 mm. To compensate the extra weight, they also proposed the abandonment of the upper casemate.371

Pitzinger in his 27 March report to the Marinesektion refl ected only on the Arsenal’s proposal. He stated that the thickening of the Mitteldeck by 20 mm would result in reducing the thickness of the main belt, the barbettes and the conning tower to 300 mm.372 It is clearly visible that Pitzinger was sticking to the upper casemate around the conning tower and its four 15 cm guns and was reluctant to sacrifi ce it, but the days of the Reduit were numbered.

Th ere were many problems with the Reduit, or upper casemate. Th e foundations of the pivots of the 15 cm guns were weak, the ammunition supply of the guns was diffi cult and the fore triple turret could block the fi re of the Reduit’s guns when it was trained to starboard or portside. Due to these problems on 15 April 1914 the Navy fi nally decided to abandon the upper casemate. With this decision the number of 15 cm guns was reduced from 18 to 14.373 Th e 470 tons weight saved by the elimination of the upper casemate was spent on armor thickening and structural reinforcements. Th e Mitteldeck over the magazines of the two triple turrets, which was an area of 1,050 square meters, was thickened from 30 to 50 mm. Th e armor of the barbettes between the armored deck and the Mitteldeck was reinforced, its thickness increasing from 80 to 110 mm. Th e transversal armored bulkheads were also reinforced as were the foundations of the conning tower and the twin turrets. Th e 11 mm plating of mild steel (Schiff baustahl) was changed to 40 mm reinforced plating of K armor above the bow and stern armor ranging to the portholes. Th e 35 cm ammunition allowance per gun once augmented from 76 to 100 rounds was reduced again to 76 due to lack of space.374 One of the reasons of the latter was the redesign of the broadside torpedo tube rooms to accommodate the longer 7 m type torpedoes.375

When the delegations voted for the extraordinary credit in May 1914, the fi nal design was ready to approve, with only one great test still remaining: the underwater explosion test on a test bed which represented the 1/1 scale midship section of the projected battleships.

Th e Underwater Explosion Test

It is matter of common knowledge that the defi ciencies of torpedo protection system of the Tegetthoff class dreadnoughts moved the Austro-Hungarian Navy to carry out expensive underwater tests following the German example.376 To evaluate the layout of torpedo protection (torpedo bulkhead, armored deck) a 1/1 scale test bed, a hull middle section, the so called Sprengobjekt (explosive object) was constructed. All test reports were, however, disappeared from the Kriegsarchiv Vienna, allegedly an Allied fact fi nding team of unknown nationality carried them away and consequently the results of the test remained unknown for a long time. Fortunately, in the Archives of the Technical and Transport Museum of Budapest, some documents of the abovementioned underwater test were found including the test report.377

When Haus replaced Montecuccoli as Marinekommandant the Navy recognized the immense importance of the underwater protection against naval mines and torpedoes. In the light of the wellknown defects of the torpedo protection system of the Tegetthoff class battleships now under construction the Navy was no longer satisfi ed with theoretical calculations and useless experiments on models. In 1913, the Navy decided, possibly on Haus’s direct order, to execute an expensive underwater test on a test bed representing a 1/1 scale of the battleships to be built. It was a reasonable decision because the less than quarter million Kronen cost of the test was a fraction of the 328 million Kronen price of the four battleships all the more so because the test results could save an expensive battleship from sinking.

Th e test on a 1/1 scale section of the 24,500 ton battleship was ordered by the Navy on 9 September 1913. Th e MTK completed the plans for

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49 Th e plan of the Sprengobjekt, the test bed for evaluating the torpedo protection system of the 24,500 ton battleship design

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the 450 ton Sprengobjekt by November 1913. Th e 7.87 m long, 8.24 wide and 11.22 m high Sprengobjekt represented a six frame-long boiler room section of the 24,500 ton battleship. Th e empty weight of the Sprengobjekt was 133 tons, 61 tons of armor plates represented the belt and 51 tons of armor was used on the other side as counterbalance. Th e space between the torpedo bulkhead and the double hull contained 64 tons of coal (briquette). 87 tons of additional ballast and 54 tons of water were in the double bottom and double hull cells to trim the Sprengobjekt. Th e written documents mention a coaling door cut in the torpedo bulkhead, but this door not visible on the plans.378

During the preparation work for the test, the Marinesektion asked the Germans for detailed information on the German tests. In their answer of January 1914, the Germans said that they would transfer data only if the test would be carried out in accordance with German specifi cations. Th e MTK concluded that in this case it had to construct a Sprengobjekt nearly twice as large as originally planned. Th e MTK put forward a compromise proposal to carry out two tests, one with the original and one with the larger test bed, the latter test with a greater explosive load. On 8 April 1914, Haus decided to execute the test as originally had been planned. He explained his decision with the shortness of time and with the lack of the Navy’s means to salvage the larger test bed after the test.379

It was originally planned that the test would be executed by a naval mine simply bolted to the side shell plating 4.2 meters below the waterline, but the 8 March 1914 order of the Navy decided instead for a 45 cm torpedo warhead fi lled with 110 kg T-Ammonal (amatol). Th e torpedo warhead could be lowered in a cage on two vertical rails by a davit. Th e Navy also wanted to examine the impact of the detonation on diff erent explosives and propellants, so for this purpose sixteen small metal boxes fi lled with diff erent types of M/97 propellant, TNT, ecrasite, etc., were bolted to the inner side of the torpedo bulkhead.380 Th e Sprengobjekt was built in the Pola Arsenal in the late spring of 1914.

On the order No 157 of the Hafenadmiralität (Harbor Admiralty) of Pola of 6 June, the test was executed at 2 p.m. on 10 June 1914. In the morning of 10 June, the Sprengobjekt was towed from the Arsenal to the Valmaggiore Bay where it was moored 3.1 km from the pier from which the committee observed and fi lmed the experiment. At 2:30 p.m. the warhead was ignited by an electric cable. Th e splash caused by the explosion was 70 m high. Th e Sprengobjekt sank in 28 minutes. On the next day the wreck lying on the seabed was examined by a diver. On 15 June, the wreck was salvaged by the 240 ton fl oating crane of the Arsenal and was carried to Dock No 22 for examination.381 It’s more than probable that the experienced naval architects and engineers of the MTK and the Arsenal saw at the fi rst glance that the experiment was successful and the protection system worked well. It is almost certain that they immediately informed Haus and the Marinesektion of the success of test. Th e wreck of the Sprengobjekt was thoroughly examined and the committee made its report on 3 July.

Th e committee pointed out in its 3 July offi cial report that the test was a defi nitive success, as the torpedo bulkhead and the armored deck remained watertight. Th e lower layer of the armored deck was tore away by the explosion over the double hull, but the upper layer remained watertight. Th e armored deck over the reserve coal bunker remained almost intact deforming only slightly. Th is throws light upon the other, less known defi ciency of the underwater protection system of the Tegetthoff class discussed in details in the chapter on the given battleships. Th e explosion caused only small dents (max 80 mm) in the torpedo bulkhead. Th e armored coaling door cut in the torpedo bulkhead also remained watertight. Th e propellants and the explosives attached to the inner side of the torpedo bulkhead did not explode. Th e brief summary of the test report stressed: “On the basis of the experiment it can be stated that a ship constructed this way will not be endangered by a 110 kg 45 cm torpedo warhead and the resulting list of 2 degrees can easily be compensated.”382

In 1914, the Navy also conducted so-called “caisson tests”. Th e main purpose of these tests was obtaining data for more precise calculations which would help to design improved watertight bulkheads. Th e tests were executed on the ½ scale models of the watertight bulkheads used on the Tegetthoff class. Th e test results were not very promising for the Tegetthoffs: converting the data to 1/1 scale bulkheads the engineers of the MTK came to the conclusion that the pressure of a 5-6 m high water column could cause a 30 cubic meters per hour leakage through the bulkhead.383

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50 Th e salvaged Sprengobjekt after the test in the Floating Dock No 22

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