The Naval Law stipulated that the lifespan of large warships was to be reduced from 25 years to 20 years; this was done in an effort to force the Reichstag to allocate funds for additional ships. The reduction necessitated the replacement of the coastal defense ships of the and classes as well as the s. The battleships that Tirpitz had failed to secure in the First Amendment to the Naval Law of 1906 were now approved by the Reichstag. The Naval Law also increased the naval budget by an additional 1 billion marks. After the four s had been replaced by the four "Nassau"s, three of the "Siegfried"-class ships—, , —and the unique coastal defense ship "Oldenburg" were the next slated to be replaced. The "Helgoland"-class ships—SMS "Helgoland", SMS "Ostfriesland", SMS "Thüringen", and SMS "Oldenburg"—were ordered under the provisional names "Ersatz Siegfried, Ersatz Oldenburg, Ersatz Beowulf," and "Ersatz Frithjof", respectively.