The deal is a follow on to an earlier deal to buy eight P-8I aircraft, which had an option for buying four more additional aircraft later.
The cost of the deal was not revealed. Deliveries of the aircrafts are expected over next three to four years.
The P-8I Long Range Maritime Patrol aircraft stationed at INS Rajali, Arakkonam, has been called one of the best maritime surveillance aircrafts in the world.
Equipped with foreign and indigenous sensors for maritime reconnaissance, anti-submarine operations and electronic intelligence missions, the aircraft is fully integrated with state-of-the-art sensors and highly potent anti-surface and anti-submarine weapons.