India announced yesterday that its first domestic nuclear submarine was ready for sea trials, a step before it becomes fully operational, and called it a "giant stride" for the nation. India unveiled the 6,000-tonne INS Arihant ("Destroyer of Enemies") in 2009 as part of a project to build five such vessels armed with nuclear missiles and torpedoes. Prime Minister Manmohan Singh said he was "delighted to learn that the nuclear propulsion reactor on board INS Arihant, India's first indigenous nuclear powered submarine, has now achieved criticality". Criticality refers to the point at which a nuclear reaction is self-sustaining. Singh described the development as "a giant stride in the progress of our indigenous technological capabilities" and said he hoped to see the submarine commissioned soon. Arihant is powered by an 85-megawatt nuclear reactor and can reach a speed of 44km/h, according to defence officials. It will carry 95 crew. The reactor on board the INS Arihant was activated earlier, paving the way for the commencement of sea trials. The Indian navy put a Russian-leased nuclear submarine into service in April last year, joining China, France, the United States, Britain and Russia in the elite club of countries with nuclear-powered vessels. Nuclear submarines can function under water without needing to surface regularly to be recharged or refuelled, unlike their conventional diesel-electric counterparts. India is due to receive the first of six Franco-Spanish diesel-electric Scorpene submarines in 2015, part of a multibillion-dollar project to modernise its navy. The submarine announcement came on the eve of the launch of India's first indigenous aircraft carrier, the INS Vikrant. The navy will launch the 40,000-tonne Vikrant tomorrow in the port city of Kochi, making India only the fifth country in the world that has the capability to build such vessels. It will be deployed after fitting out in 2018.