guns for use against small and fast vessels such as torpedo boats and submarines. Furthermore, she also fitted with four submerged torpedo tubes, one each in the bow, the stern, and each side. Complementing these torpedo tubes, Prinz Eugen usually carried twelve torpedoes. Armor Prinz Eugen was protected at the waterline with an armor belt which measured thick in the central citadel, where the most-important parts of the ship were located. This armor belt was located between the midpoints of the fore and aft barbettes, and thinned to further towards the bow and stern, but did not reach either. It was continued to the bow by a small patch of armor. The upper armor belt had a maximum thickness of , but it thinned to from the forward barbette all the way to the bow. The casemate armor was also thick. The sides of the main gun turrets, barbettes, and main conning tower were protected by of armor, except for the turret and conning tower roofs which were thick. The thickness of the decks ranged from in two layers. The underwater protection system consisted of the extension of the double-bottom upwards to the lower edge of the waterline armor belt, with a thin plate acting as the outermost bulkhead. It was backed by a torpedo bulkhead that consisted of two 25-millimetre plates. The total thickness of this system was only which made Prinz Eugen incapable of containing a torpedo warhead detonation or mine explosion without rupturing. This design flaw would ultimately prove to be fatal to her sister ships Szent István and Viribus Unitis. Construction Montecuccoli's plans for the construction of Prinz Eugen and her sister ships earned the approval of Emperor Franz Joseph I in January 1909, and by April plans for the design and construction of the ship was laid out. Roughly a year after Prinz Eugens plans were drafted, Arbeiter-Zeitung, the Austrian Social Democratic Party newspaper, reported the details of the battleship to the general public. The Christian Social Party, supportive of the construction of Prinz Eugen and her sister ships, and operating on the advice of the navy, published in its own newspaper, Reichspost, that the secret project to construct the ships and the related financial agreements to fund the first two were true. The Reichspost lobbied in support of the project, citing Austria-Hungary's national security concerns with an Italian dreadnought already under construction. When the