US Defence Secretary Robert Gates has arrived in Delhi on a two-day visit aimed at bolstering military ties and promoting US arms manufacturers.
Robert Gates has praised India's deepening ties with the US
US firms are competing with Russian and European rivals for a multi-billion dollar deal to sell India fighter jets.
Mr Gates has said he wants to "expand" India's "significantly improved relationship" with the US. India has largely relied on Russian arms imports.
India meanwhile says it successfully tested a new type of ballistic missile.
The nuclear-capable missile was launched from an underwater platform off the south-eastern coast of India, a defence ministry official told the AFP news agency.
The new missile is expected to serve a nuclear submarine being built by India.
Mr Gates is expected to spend his two-day visit lobbying for US firms that hope to win a contract to supply India with 126 new fighter jets.
US firms such as Lockheed are hoping to secure deals in India
US-based Lockheed and Boeing are competing for the deal, valued at between $10bn-$12bn.
Other firms fighting for the contract include Russia's Mig, France's Dassault, Sweden's Saab and the Eurofighter consortium of British, German, Italian and Spanish companies.
The deadline for the bids expires next week.
A US official told Reuters news agency Mr Gates would aim to show that Americans offered not only the best product but the best maintenance package too.
US firms "operate with integrity", the official said, "which is different than what India has seen with other partners in the world".
Speaking before his visit, Mr Gates said the improved relationship between India and US had been one of the most significant changes since he was last in government 15 years ago.
"I want to see what we can do to not only strengthen that [relationship] but perhaps expand it in other ways," he said.
Defence co-operation between India and the US has increased dramatically since the end of the Cold War, with both countries seemingly driven by a desire to check China's growing military influence.
India earlier this month agreed a $1bn deal to buy military transport aircraft from US firm Lockheed Martin.
However, a key deal that would see the US supply India with nuclear technology for civilian uses has yet to be approved by India.
The deal, which would end a three-decade US ban on nuclear exports to India, is opposed by the Indian government's communist allies.