These characteristics have made nuclear submarines strategic weapons of deterrence and they play a key role in national defense. By owning a nuclear submarine fleet, a nation can almost guarantee it will have the ability to respond in case of attack, thus deterring possible rivals from launching any strikes.

This is the reason why the world's major powers have all developed and upgraded their nuclear submarines. All the five permanent members of United Nations Security Council, namely the US, Russia, the United Kingdom, France and China, have nuclear submarines, and India began sea trials of its first indigenously built nuclear submarine, INS Arihant, in August.

China started its nuclear submarine program in the 1960s and its first nuclear submarine made maiden voyage in 1970. In the days of the Cold War, nuclear submarines were of key importance in preventing nuclear blackmails by the US and former Soviet Union, both of which were antagonist toward China.

Besides, having suffered repeated invasions from the sea in modern times, China wanted a strong navy and nuclear submarine fleet to act as deterrents to any future invasions.

Therefore, since it was first commissioned, China's nuclear submarine force has been clearly labeled "defense only"; this is in accordance with its military strategy, which is purely defensive in nature.

With some countries keen to play up "China threat" for their own purposes, there have been exaggerated reports of the power of China's nuclear submarine fleet in the Western media, some of which even claim the submarines can carry ballistic missiles with nuclear warheads and can target distant countries. But China's position on nuclear weapons is extremely clear: no first use of nuclear weapons, no use or threat of use of nuclear weapons against non-nuclear states, no export of nuclear weapons materials and technology.

These principles apply to nuclear submarines or nuclear missiles, too.

The US and Russia have the most advanced nuclear submarines, while the UK and France have the second best; China's nuclear submarine technology lags behind all of them, especially in their information and power systems. So it is ridiculous to talk an inferior member of the nuclear submarine club being a threat.

China adheres to a national defense principle of self-defense. For those who have no intention of harming China's territorial integrity and sovereignty, China's nuclear submarines are really nothing to worry about. Nuclear submarines serve the role of deterrence, and China will not easily resort to them unless under attack.

The author is director of Naval Research Institute of the People's Liberation Army. This is an excerpt of his interview with China Daily's Zhang Zhouxiang.

(China Daily 10/31/2013 page9)