India has signed a $2.1 billion contract with leading US aircraft manufacturer Boeing Co. for naval patrol aircraft as part of an overhaul of the South Asian nation's mainly old Soviet military hardware. India, fast becoming one of the world's biggest arms importers, said at least eight of the P-8I anti-submarine and anti-surface warfare planes would be delivered in four years. “The deal has been signed and the delivery of the P-8I should start in four years' time,” defense ministry spokesman Sitanshu Kar said on Monday. India is looking to spend $30 billion on imports over the next five years to modernise its largely Soviet-era arms and is also trying to strengthen its navy by introducing new weapons systems. Boeing plans to make inroads into the South Asian defense market and has already submitted a bid for a contract to supply India with 126 multi-role fighter jets, potentially worth more than $10 billion. Last July, Boeing said it would bid for defense projects in India worth up to $20 billion over the next 10 years. India is also keen to strengthen its own aerospace industry and has asked major weapons exporting countries to transfer defense technology to India. Defense experts said the P-8I would give India an edge over its rivals. The aircraft would carry air-to-surface missiles as well as anti-shipping missiles to tackle sea-based threats, a defense official said. A Boeing spokesman said the company would release a detailed statement on the deal in two days.