ST. PETERSBURG, November 12 (RIA Novosti) - A Russian Delta-IV class Karelia nuclear submarine has started sea trials following lengthy modernization at the Zvezdochka shipyard in northern Russia, the company said.

The overhaul, which started in 2004, included noise reduction, improved enemy ship and submarine tracking capabilities, and enhanced survivability. The submarine has been equipped with 16 Sineva RSM-54 missiles.

K-18 Karelia could join Russia's Northern Fleet by the end of this year, the shipyard said in a statement on Wednesday.

Similar overhaul has been done to four other Delta-IV class submarines - the K-51 Verkhoturye, the K-84 Yekaterinburg, the K-114 Tula, and the K-117 Bryansk.

The Russian Navy has seven Delta-IV class submarines in service. They are all deployed in the Northern Fleet.

"The Delta-IV class submarines are the core of the naval component of the Russian nuclear triad at present. After the modernization, the subs will be able to remain in service for another 10 years," Zvezdochka said.