These are the same Cold War calculations that the U.S. and Soviet Union were making in the 1950’s and 60’s, but they are just as relevant today.

Mounting concern within the People’s Liberation Army’s (PLA) over the vulnerability of its land-based nuclear deterrent and the ability to deliver a retaliatory second strike has prompted China to place some of its nuclear warheads on board submarines.

Two years ago, China deployed the Jin-class ballistic missile submarine for the first time, each armed with 12 JL-2 nuclear missiles.

Operating from a state-of-the-art base near Sanya, on Hainan island’s southernmost tip, Jin class submarines are now patrolling the depths of the South China Sea. But in order to be within range of the US, they must be able to break out into the Pacific Ocean.

Before the submarines achieve this, they must leave their base in Hainan and cross the South China Sea to reach the Pacific Ocean undetected. The Pentagon believes that the first such Pacific patrol will occur this year.