In the eastern theatre of the war, the Indian Eastern Naval Command completely isolated East Pakistan by a naval blockade in the Bay of Bengal, trapping the Eastern Pakistani Navy and eight foreign merchant ships in their ports. From 4 December onwards, the aircraft carrier was deployed, and its Sea Hawk fighter-bombers attacked many coastal towns in East Pakistan including Chittagong and Cox's Bazar. Pakistan countered the threat by sending the submarine , which sank en route under mysterious circumstances off Visakhapatnam's coast On 9 December, the Indian Navy suffered its biggest wartime loss when the Pakistani submarine sank the frigate in the Arabian Sea, resulting in a loss of 18 officers and 176 sailors.