In the 1890s the priority of the fortification works in the Baltic Sea had been the protection of the ice-free port of Liepāja, and the Kronstadt fortress protecting Saint Petersburg, relegating Viapori to a secondary status. After the losses during the Russo-Japanese War and in light of the rising might of the Imperial German Navy, Liepāja was considered too vulnerable for a main fleet base, and the decision to build Peter the Great's Naval Fortress was made. In the new plans the main line of defence against the enemy was at the Porkkala-Tallinn line with Tallinn also the new main base for the Russian Baltic Fleet. Helsinki was to be a base for torpedo boat flotillas. The construction of the Tallinn naval base was delayed however, and with the new ships being constructed to replace the losses suffered against Japan the Russian Navy was forced to rely more on Helsinki despite the obsolete armament and inadequate fortifications at Viapori. As the threat of war in Europe grew, it became essential to expand the fortress to provide a necessary protection for the naval base. Until 1910, when the first 152 mm Canet guns arrived, the only modern weapons at Viapori were 57 mm quick fire guns with the rest of the artillery designs dating from the Russo-Turkish War. The first new 254 mm guns arrived in 1913, but it was not until early 1914 that construction of the first new batteries began on Melkki and Isosaari. During the First World War the new Krepost Sveaborg was built to substantially expand the old fortress. A new main line of defence was constructed on the outlying islands, pushing the defensive line several kilometers southward, thus providing a secure outer anchorage south of the old fortress for larger warships without the need to navigate the narrow straits leading to the inner anchorage at Kruunuvuorenselkä. The older parts of the fortress became a second line of defence and the main storage areas. The rear of the fortress was finally protected by land fortifications, at first field fortifications on the Helsinki peninsula built in 1914, and, later, an outer line of fixed fortifications.
