Answer by Chait Belwal:
Before the 1971 India-Pakistan war, Indian Navy’s (IN) sole aircraft carrier INS Vikrant was docked in Visakhapatnam at the eastern coast of India. After the 1971 hostilities started, Indian naval intelligence got wind of Pakistani plans to target the Vikrant through its flagship submarine PNS Ghazi which was a Tench-class diesel-electric submarine leased from the US Navy. During the initial days of the war the IN stealthily moved Vikrant to a secret harbor (Port X-Ray) in the Andaman and Nicobar islands. However, it wanted the Pakistani Navy (PN) to think the Vikrant was still in Visakhapatnam. To do this, every week large orders for groceries were made from the IN’s port in Visakhapatnam. These orders were large enough to sustain the 1,340 sailors of the INS Vikrant, and to any observer (including Pakistani spies) it meant the Vikrant was in Visakhapatnam. Another ship INS Rajput was used as a decoy for INS Vikrant, and several wireless transmissions were made to/from INS Rajput (a larger ship has more wireless messages). A deliberately unencrypted telegram was also sent wirelessly through INS Rajput in the name of a sailor from INS Vikrant asking about the health of his mother who had fallen seriously ill.
Pakistani Navy took the bait and sent PNS Ghazi off the harbor entrance in Visakhapatnam, where she was sunk by depth charges of IN ships , becoming the only submarine sunk in war after World War II. The hull of the submarine still lies in the sea bed off the Visakhapatnam coast. INS Vikrant continued on to southern East Pakistan (now Bangladesh) and played a pivotal role in the destruction of PN ports and ships.