China's "marine corps" has been misunderstood for decades. Until the
1980s, the Chinese didn't have a marine corps, only army units that were
trained to conduct amphibious operations. China didn't start building its own
large amphibious ships until the 1980s, at the same time they organized marine
brigades. There are currently two of these, containing a total of 6,000 troops.
Interestingly, the marines are not stationed where they could be used for an
invasion of Taiwan, but in the south, where they can grab disputed islands.
While these islands, which control fishing and potential oil fields, are
considered disputed, China has already laid claim to some of them by force. In
1974, China fought a naval battle with the Vietnam off the Paracel islands. In
1988, China and Vietnam fought another naval battle, off the Spratly islands.
Both of these battles were followed by Chinese troops establishing garrisons on
some of the islands. In 1992, Chinese marines landed on Da Lac reef, in the
Spratly Islands. In 1995, Chinese marines occupied Mischief Reef, which was
claimed by the Philippines.
Chinese marines are trained and equipped for raiding, not for large scale
landings against a defended shore. The latter task is apparently left to army
divisions that have been drilled on how to get on, and off, amphibious ships.
While the Chinese marines might play a part in a Taiwan invasion, their full
time job appears to be in the South China Sea, where the Chinese stand ready to
grab more islands, if the economic advantages seem high enough.