India on Wednesday signed a $1-billion contract with Boeing Co to buy four long-range P-8 maritime spy aircraft, Reuters reported. Two officials from the Defence Ministry and an industry official told the news agency that the deal is aimed at boosting the Indian Navy's efforts to check China's presence in the Indian Ocean.

The contract was signed during a visit by Frank Kendall, the United States Undersecretary of Defence for Acquisition. An official said it was a "follow-on order", while another confirmed the value and added that the planes are expected to come into use over the next three years.

Eight such long-range P-8 aircraft have already been deployed by India to monitor movements of submarines in the Indian Ocean. The move indicates India's attempt to further strengthen its Navy, given China's increasing naval expansion in the ocean.

A spokesperson for Boeing defence, space, and security in India, Amrita Dhindsa, said that besides long-range patrol, these spy planes also have Harpoon missiles for anti-submarine warfare. She declined to comment on the deal.