A US Navy carrier group along with warships from India and Japan are engaging in submarine warfare, air defence, search and rescue exercises in the Philippine Sea, reports the Wall Street Journal.
The Philippine Sea, windward of Taiwan, east and northeast of the Philippines covers five million square kilometres.
The international flotilla is a demonstration of the united naval power of the Asia Pacific democracies contending with a more assertive and well-armed China, said the WSJ report.
Washington and Tokyo have long co-operated on defence and the US has been working on deepening strategic co-operation with India, encouraging New Delhi to be a more active naval presence beyond the Indian Ocean.
"Americans are looking for those who can share the burden," said Rja Mohan, director of the Carnegie Endowment for International Peace's India Centre. A strengthened three-way partnership among the US, Japan and India is "an important strategic shift".
Cementing those relationships has been a US objective as it grapples with what Americans call China's growing militarisation the South China Sea where Beijing is embroiled with disputes with it neighbours and is building up artificial islands with runways capable of landing military aircraft.
The US has sent warships and planes in a series of operations to Chinese claims, saying its aim is to ensure freedom of navigation in waters that carry one third of global trade.
During Indian Prime Minister Narendra Modi's US visit last week, he said: "The absence of an agreed security architecture creates uncertainty" and that a strong partnership would help freedom of navigation.
India contributed two stealth frigates, a guided missile corvette and a support ship to join the multiday Malabar exercises, part of annual US-Indian exercises that have become increasingly sophisticated.
Ahead of the exercises Indian warships made port calls in Vietnam and the Philippines, both of which have disputed Chinese South China Sea claims