Two years ago, commercial
satellite photos began to show details of a submarine base that China was
building at Yulin, near Sanya, on the southern island of Hainan (near Vietnam).
The base has underground docking facilities for nuclear and diesel-electric subs,
created by tunneling into coastal hills. Rumors of such a base have been
circulating for the past six years, apparently since locals began noticing all
the construction activity, and the tight security around the site. The
underground facilities not only protect the boats from air or sea based attack,
but enable maintenance and modifications to be done in secret.