60,000 litres of oil removed from wreck of coastal defence ship Ilmarinen

The coastal defence ship Ilmarinen, which sank off the island of Utö during World War II, is one of the shipwrecks that are hazardous to the Baltic Sea environment. The environmental risk is posed by the oil in the vessel’s fuel tanks, the amount of which is estimated to be approximately 100,000 litres in total.

The emptying of the Ilmarinen’s tanks, which began in mid-July, went well even though not all of the oil could be recovered yet. A total of approximately 60,000 litres of oil, mostly light fuel oil, could be removed from the wreck.

“The operation as a whole was successful, even though we had to interrupt our work for three days because of the rough seas and retreat to the archipelago for shelter. The operation also had to be finished approximately one day earlier than planned because of the roughness of the sea,” says Project Manager Tommi Kontto from the Finnish Environment Institute. “Considering this, we worked quite efficiently. Oil was removed from the tanks on the bow side of the Ilmarinen, and the risk of a major environmental accident caused by the possible collapse of the bow could be reduced significantly.”

According to Commander Toni Joutsia, Chief of Staff of the Coastal Fleet, the operation was an extremely demanding task: "There is 60–80 metres of water at the site where the Ilmarinen sank. It sets very strict safety requirements for the equipment, the diving activities and the operations on the surface. The Ilmarinen lies upside down on the seabed, its keel towards the surface. We were able to pump oil directly from the tanks through the holes we had drilled to the bottom of the vessel,” says Commander Joutsia.

The Coastal Fleet led the operation together with a coordinator from the Finnish Environment Institute. The multipurpose vessel Louhi and the oil recovery vessel Halli were used in the operation. The Finnish Border Guard prepared for preventing environmental damage with its air and surface assets. The Diving Medical Center of the Defence Forces participated in the operation to safeguard the wellbeing of the Navy divers. In case there was an accident, the Center had a decompression chamber, a doctor, a diving nurse and a field nurse ready on the multipurpose vessel Louhi.

“I must say that the professionalism and seamanship of the maritime authorities is at a high level. Each activity had been well planned and practised both on the surface and in the depths. On behalf of the operation, we would like to thank everyone who travelled at sea for letting us work undisturbed in the area,” says Commander Toni Joutsia.

The emptying of the wreck will continue next year

It is estimated that 40,000 litres of oil still remains in the wreck of the Ilmarinen. The aim is to continue the work in 2027.

Sari Multala, Minister of Climate and the Environment, is pleased that the Ilmarinen now poses a significantly lower risk to the Baltic Sea environment as a result of the operation. “It is important to complete the oil removal,” emphasises Minister Multala.

“Before this, four high-risk shipwrecks in the Baltic Sea had already been cleaned up in the Hylky project. It is great that these operations have strengthened the authorities’ competence and readiness to carry out such demanding tasks and act in such challenging conditions,” says Minister Multala.

The Ministry of the Environment funds the removal of oil from the wreck of the Ilmarinen from the Ahti Programme (2023–2027) aimed at improving the state of waters and marine areas. Among other things, the funding has been used to procure special equipment suitable for the operation for the use of the Navy.

The leak has been located to corroded rivets in the hull

Before the removal of oil, the Finnish Environment Institute investigated the wreck of the Ilmarinen several times and carried out a risk assessment on it. The investigations have shown that the wreck is leaking fuel oil at the rate of 1–2 drops per minute. During the operation in July, the leak was located to the riveted joints in the hull of the vessel, which have been affected most by corrosion.

"Each wreck is unique and individual. The wreck and the conditions must be examined carefully. The work must be planned and the equipment selected carefully so that oil can be removed safely both from the point of view of the environment and the people carrying out the work,” says Project Manager Tommi Kontto. “The Ilmarinen operation has been prepared since 2023 and it was practised in 2025 and in spring 2026. Practising has ensured the efficient and safe implementation of the task."

The wreck of the coastal defence ship Ilmarinen is located in the northern Baltic Sea, outside the territorial waters in the exclusive economic zone of Finland. Ilmarinen sank in September 1941 after having hit a sea mine. A total of 271 crew members drowned with the vessel and the wreck is their final resting place. Preserving the sanctity of the grave has been an important aspect of the operation.

“With regard to the sanctity of the grave, I can say that we were able to respect it throughout the operation. The final resting place of our marine soldiers was not disturbed,” says Toni Joutsia, Chief of Staff of the Coastal Fleet.