Via War is Boring, I see that China is putting artillery on cargo ships. (The picture on the left showcases this.) China Defense gives some possible explanations.
China Defense's two (non-exclusive) explanations, though, don't make much sense. The first is to attempt to bolster its rather weak amphibious capability, by using cargo ships to transfer people, and the artillery to protect the ships. This is an essential capability that the Chinese Navy currently lacks, especially if it wants to be able to effectively threaten Taiwan with invasion. As it stands, China cannot put enough boots on the ground fast enough to establish a beachhead against Taiwanese fire. (The Chinese can move only about 15K troops at a time, whereas the Taiwanese military can through 200K onto any of the possible landing sites in hours.)
This is pretty ludicrous, though, because that artillery won't do much good against missiles, and the ships would be close to sitting ducks versus any real anti-ship measures. Granted, there is some possibility of China establishing air superiority with a strong early missile attack, but the first priority for any ROC naval units would probably be to stop troop transports. These would all go down quick.
The second explanation seems even more bizarre: "The PRC propaganda machine is attempting to portray preparations for an impending invasion in order to deceive and/or intimidate potential target nations." Again, this could only mean Taiwan. It should be obvious to the PRC leadership, however, that attempts to intimidate Taiwanese voters tend, instead, to piss them off. Also, there is less reason to invade Taiwan now than at any point from 1996-2008. The current president is anti-independence, as is the legislature.
In short, none of this makes much sense.