In its largest defence purchase ever from the United States, India has signed a deal to buy eight maritime aircraft from aerospace major Boeing to strengthen the Navy's intelligence gathering capabilities.

The $ 2.1 billion contract for eight Boeing P-8I long-range maritime reconnaissance aircraft was signed between a defence ministry official and Boeing's country head Vivek Lall in New Delhi [Images] on January 1, Navy and industry sources said.

The government had approved the deal in its last Cabinet Committee on Security meeting in 2008 after protracted talks.

The deal with Boeing, sources said, was through a direct commercial contract and issues such as end-user verification agreement between India and the US for these defence products were still pending, sources said.

The Navy will get its first aircraft under the deal by 2012-13 and the rest of the aircraft would be delivered in phases by 2015-16, sources said.

The contract also provided for the Navy to place follow-on orders for about eight more of these aircraft, being purchased to replace the existing fleet of eight ageing Tupolev-142M turboprops.

The P-8I is armed with torpedoes, depth bombs and Harpoon anti-ship missiles and is capable of anti-submarine warfare and anti-surface warfare.

Expected to help in plugging the existing gaps in the Navy's maritime reconnaissance capabilities, the aircraft has an operating range of over 600 nautical miles.