The United States believes that China has modified at least one of its Type 93 SSN (nuclear attack) submarines so it can more effectively operate in coastal waters and deliver commando teams. The modifications include a miniature sub on deck for landing commandos and other changes to make the sub better able to operate in shallow coastal waters. All this makes sense, as it was obvious early on that the Type 93s were not as effective on the high seas as their designers and builders had hoped.
The 093 class SSNs begin to appear in 2002. This class was, like its predecessors, obsolete at birth. Work had already begun on a successor and the first of the new Type 095 class was launched in 2010 and is supposed to enter service in 2015. The lone 095 has been undergoing sea trials but there is little known about how it has performed. Meanwhile two Type 93s were completed (one of these was converted to the commando model) and four more are under construction. These four may be scrapped if the Chinese cannot come up with enough mods and tweaks to give the 93s a reasonable degree of usefulness. The coastal mod appears to be part of that effort.
The Type 093s look a lot like the Russian Victor III class, a 1970s era SSN design. And the subsequent Type 94 SSBN (ballistic missile carrying nuclear powered boat) looks like a Victor III with a missile compartment added. Taking a SSN design and adding extra compartments to hold the ballistic missiles is an old trick, pioneered by the United States in the 1950s to produce the first SSBNs. The Chinese appear to have done the same thing with their new SSN, creating a larger SSBN boat of 9,000 tons displacement. Priority was apparently given to construction of the 094, as having nuclear missiles able to reach the United States gives China more diplomatic clout than some new SSNs.
After the 7,000 ton, 093 class SSNs went to sea, China was apparently underwhelmed by their performance. Not much more is expected from the 094 SSBNs. The 093s are too noisy and have a long list of more minor defects as well. The Chinese have had a hard time building reliable nuclear subs, but they are determined to acquire the needed skills. You do that by doing it and eating your mistakes. China appears to have built five Type 094s and a sixth may be on the way.