As reported in the Indian press, on August 10, 2013 the reactor on board of India's nuclear-powered submarine, INS Arihant, reached criticality at 1:20am. The reactor is described as a pressurized water reactor with a power of about 80 MW. It was developed at the Indira Gandhi Centre for Atomic Research at Kalpakkam, which also hosts the prototype naval reactor. The naval reactors reportedly use HEU fuel with enrichment of about 30% U-235.

In addition to the indigenous INS Arihant, India operates a nuclear powered submarine INS Chakra that is leased from Russia.