The public got a rare glimpse into one of the most secret branches of China's military forces on Sunday when the People's Liberation Army Navy released a video of the training and exercises of its nuclear submarine force.

The video, called Things About the PLA Navy's Nuclear Submarines, shows crew members taking an oath while standing atop the nuclear-powered ballistic missile submarine, officers operating equipment within submarines as well as a submarine firing a torpedo.

The force's attack and ballistic missile submarines are shown sailing on the surface or taking part in a naval parade.

The video also shows China's first submerged launch of its submarine-based ballistic missile.

On Sunday, the PLA Navy celebrated the 68th anniversary of its founding. Over decades, the Navy has evolved from an antiquated, poorly equipped force into a modern and capable power.

Pictures of the nation's nuclear submarines are rare - they are one of the PLA's most powerful weapons and incorporate many military and technological secrets.

The Navy has never released information about its nuclear submarines' construction, commissioning or deployment.

The PLA Navy also released another video of the firing of various kinds of ammunition from ships, submarines and aircraft. It is filled with images of anti-ship and air defense missiles roaring away from warships with flames and deafening sounds.

The most rarely seen parts of the video include images of a submarine launching two missiles underwater as well as an H-6 bomber and a J-15 carrier-borne fighter jet delivering anti-ship cruise missiles.

The Navy published another four videos on Sunday, including one showing live-fire exercises of the PLA Navy Marine Corps and one saluting the Navy's female sailors.

On Sunday, the Navy began public tours of its first nuclear submarine - theChangzheng 1 nuclear-powered attack submarine.

The submarine, which was in active service for more than 40 years, is now displayed at the Navy Museum in Qingdao, Shandong province.

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