What are Chinese attack submarines doing in the Indian Ocean, far from China’s maritime backyard, in what is the furthest deployment of the Chinese Navy in 600 years? Two Chinese subs docked last fall at the new Chinese-built and -owned container terminal in Colombo, Sri Lanka. And recently a Chinese Yuan-class sub showed up at the Pakistani port city of Karachi.

The assertive way China has gone about staking its territorial claims in the South and East China seas has obscured its growing interest in the Indian Ocean. This ocean has become the new global center of trade and energy flows, accounting for half the world’s container traffic and 70 percent of its petroleum shipments.

China’s newly released defense white paper, while outlining regional hegemony aspirations, has emphasized a greater focus on the seas, including an expanded naval role beyond its maritime backyard. The white paper says that, as part of China’s effort to establish itself as a major maritime power, its navy will shift focus from “offshore waters defense” to “open seas protection” — a move that helps explain its new focus on the Indian Ocean, with the Maritime Silk Road initiative at the vanguard of the Chinese grand strategy. To create a blue water force and expand its naval role, China is investing heavily in submarines and warships, and working on a second aircraft carrier.