The torpedo tubes of the Okeanos are equipped in such a way that Harpoon anti-ship missiles can also be launched. In 2004 the ship was rebuilt in the Hellenic Shipyards in Skaramagas as part of the Neptun II repair and modernization program . It was equipped with two fuel cell blocks with 240 cells each. The tower had to be replaced in order to install the drive system that is independent of the outside air . The old tower now stands in Flisvos Park in the Athens suburb of Paleo Faliro as part of a naval memorial dedicated to the fallen submarine officers and NCOs.
The conversion was associated with many problems and for this reason the Neptune II program was probably discontinued two days before the modified Okeanos were launched in February 2009. Originally it was planned to convert further submarines of the Poseidon class. Instead, two more ships in submarine class 214 were ordered in 2010 .
