The Mumbai, an Indian warship, was slicing through choppy monsoon seas one recent morning when a helicopter swooped in overhead. Commandos slithered down a rope, seizing control of the destroyer.

It was a drill, Indian soldiers taking over an Indian ship. But the purpose was to train them to seize other countries’ ships in distant oceans, a sign of a new military assertiveness for the world’s second-most-populous nation.

India, which gave the world the idea of Gandhian nonviolence, has long derided the force-projecting ways of the great powers. It focused its own military on self-defense against two neighbors, Pakistan and China.

“India sees itself in a different light — not looking so much inward and looking at Pakistan, but globally,” said William S. Cohen, a secretary of defense in the Clinton administration who in his new role as a lobbyist represents American firms seeking weapons contracts in India. “It’s sending a signal that it’s going to be a big player.”

India is buying armaments that major powers like the United States use to operate far from home: aircraft carriers, giant C-130J transport planes and airborne refueling tankers. Meanwhile, India has helped to build a small air base in Tajikistan that it will share with its host country. It is modern India’s first military outpost on foreign soil.

India’s buildup has several overlapping motivations. It now trades vigorously with the world, most critically in oil. It has bought oil fields or engaged in exploration in Iran, Iraq, Libya, Russia, Sudan, Syria, Vietnam and beyond. Not coincidentally, it has demonstrated a new interest in keeping the sea lanes through which that oil and other wares sail free of pirates and militants.

A more robust military is also vital for protecting millions of Indian workers in the Persian Gulf, who are from time to time threatened by political volatility. But the most pressing motivation may be the fast-moving Chinese.