C-Lion1 submarine cable, also known as Sea Lion,  is a 4-fiber-pair and 1175km submarine cable from Helsinki in Finland to Rostock in Germany under the Baltic Sea, being the first direct submarine cable link between the Nordic region and continental Europe.

C-Lion1 (Sea Lion) provides a direct, low latency and cyber secure Internet backbone connection between Finland and Germany, Before the completion of C-Lion1, all data transmission to Finland has taken place via Denmark and Sweden.

Cinia Group leads the Sea Lion initiative as the developer and builder of the submarine cable, and later as an open access network operator. The Finnish Government is an enabler and investor of the initiative together with institutional investors OP-Pohjola and Ilmarinen. Investments with equity and debt financing will total at approximately 100 million Euros. The sea cable initiative is designed to meet the commercial terms and moderate profitability as long term infrastructure investment, bringing also significant direct and indirect economic benefits such as decisions by international data center operators and data intensive organizations to locate their operations in Finland.

The Finnish Ministry of Transport and Communications finalized the feasibility study on the C-Lion1 (Sea Lion) undersea cable project in June 2012. In August 2015, the Finnish government approved the construction of the C-Lion1 cable system. And Sea Lion cable project was completed in early 2016.

The C-Lion1 cable project is  supplied by ASN, with a total cost of approximately Euro 100 million.