India, Japan and the United States have sent some of their largest warships and submarines in the Indian Ocean for naval exercises. The yearly exercises have expanded in the past two years. They are a sign of deepening military cooperation among the three countries. In recent years, U.S. and other officials have expressed concerns over Chinese activities not just in South China Sea, but also in the Indian Ocean. The naval operation is the clearest sign of India’s growing security ties with the United States. Indian Prime Minister Narendra Modi and U.S. President Donald Trump confirmed those ties during their talks in Washington last month. The week-long exercises, called the Malabar exercises, began Monday on the high seas. They involve more than 15 warships, including the U.S. Navy’s nuclear-powered aircraft carrier, the USS Nimitz.