Reposaari fortress is a coastal defence system in Reposaari, Pori, built in the 1930s. The fortress is situated in the southern part of the island, west of the Reposaari village. In total, the area covers approximately 20 hectares.
The fortress comprises two gun emplacements, two ammunition warehouses, three crew and medical bunkers, fire control post, observation tower and trenches connecting them. The concrete gun emplacements, ammunition warehouses and fire control post are original. The wooden bunkers and observation tower were rebuilt in the 1990s and 2000s, as were the timber walls of the connecting trenches.
The fortress was originally the coastal battery of the Reposaari naval civil guard, and it was built by volunteers in 1935. The construction of the battery was funded by Werner Hacklin, and as far as is known, it is the only privately funded coastal battery in Finland. Its purpose was to protect the port of Pori, as well as the city itself. The battery was controlled by the naval civil guard until the mobilisation of autumn 1939, when the Finnish Defence Forces assumed its control. At the same time, the battery was expanded into a fortress.
During the Winter War, the coastal batteries of the area succeeded in downing a Russian bomber west of Reposaari. The Reposaari battery also harassed the enemy squadrons carrying out mining and bombing flights on several occasions.
During the Continuation War, the fortress was armed with four Swedish 76 K 02 field guns. There were three Canet 152/45 C coastal guns outside the fortress. In addition, there were two 87 K 95 field guns in the vicinity. However, they did not take part in the war effort.
The fortress was under the control of the Defence Forces until 1964, when it was disarmed. Two Canet guns remained, with test firing taking place until the late 1980s. Both guns remain in place preserved. The deteriorated fortress was renovated for the first time in 1992 and again in 2007–2008.