FOCSOUTH's responsibility was to interdict enemy shipping between the two wings of Pakistan and thus prevent any seaborne reinforcement of the East Bengal garrison. When war broke out, AMBA was deployed east of Ceylon whilst GODAVARI and GANGA were patrolling across the route from Colombo to the 8 and 9 Degree Channels.

On 4 December, GODAVARI captured Pakistani merchant ship PASNI and sent her under escort to Cochin. Interrogation of the PASNI's crew indicated that Pakistani merchant ships had been instructed to use the 8 Degree Channel. AMBA was therefore redeployed to the west of the 9 Degree Channel from which position she could cover all ships making for either the 8 or 9 Degree Channels.

On midnight of 12 December, AMBA detected two contacts near the 9 Degree Channel heading southeast at high speed. Air reconnaissance the next day revealed these to be British warships, one of which was the aircraft carried ALBION. Since Naval Headquarters were aware of the movements of this force, further action became unnecessary.

In the course of their patrols during the war AMBA, GODAVARI and GANGA interrogated a total of 144 neutral merchant ships for contraband and cleared them as not bound for Pakistan ports.