INS Arihant completed its maiden deterrence patrol, meaning that the submarine is fully ready for its role as a strategic deterrent. The Arihant's month-long deployment compares favourably with submarines of the US Navy which go on patrols from 30-70 days. A second SSBN has reportedly completed sea trials. Named INS Arighat, the vessel is due to be delivered next year and is expected to be double the Arihant's displacement at 12,000-13,000 tonnes, with a complement of eight K-4 missiles. Another two vessels after Arighat are planned to be commissioned by 2023. At the same time, India will require a complementary fleet of ship submersible nuclear (SSN) submarines - these are fast, hunter killer subs that will be required to detect and track undersea activity and warships.