I came across this term when reading Shui Hu Zhuan (Water Margin) novel. "Meng2 Chong1 艨艟" seems to be a kinda battleship according to my dictionary.

Does anyone has any info or picture about this battleship? When did this battleship appeared in chinese history?

The first references to the mengchong are in 2nd and 3rd century works, but the first account of such ships in action are in the Sanguo Zhi. It was a kind of warship used in battles on the Yangzi River by the forces of Liu Biao and Sun Quan. The fireships Huang Gai used to set Cao Cao's fleet on fire at Chibi were mengchong ships. When Sun Quan attacked and captured Jiangxia from Huang Zu shortly before Cao Cao's conquest of Jingzhou, Huang also tried to defend the entrance to the Han River by mooring two mengchong ships across it and putting a thousand crossbowmen on board. The name mengchong literally means 'covered charger', but almost nothing is known about what it looked like during the late Eastern Han and Three Kingdoms period.

A type of warship called the mengchong is later described in a military treatise of the Tang period - the Taibai Yinjing. These were fast, sleek vessels with an enclosed cabin for oarsmen and another covered fighting deck above that, from which crossbowmen and spearmen could strike at the enemy through open ports. The top covering for the fighting deck was apparently made of ox leather and fireproofed by dousing it with water.

Rafe de Crespigny, in "Generals of the South: The Foundation and Early History of the Three Kingdoms State of Wu" (1990), argued that the mengchong of the Sanguo Zhi was different from that of the Taibai Yinjing: while the Tang version of the mengchong was a light and fast vanguard ship, the Han and Three Kingdoms mengchong "was a powerful warship, possibly equipped with a ram, whose effectiveness depended upon the weight of its approach, not its speed."

De Crespigny's theory is based on the use of mengchong ships as floating fortresses by Huang Zu, rather than as swift attack vessels. But he does not address the question of why Huang Gai would use large, slow, lumbering ships to make a fire attack on Cao Cao's fleet. I also disagree with his suggestion that the mengchong of the Han and Three Kingdoms period may have had a ram - as far as I know there is no evidence for ramming tactics in naval warfare of that period, and de Crespigny himself admits this.

The black and white picture comes from Wu-Jin-Zon-Yau in 11th century, and the color one is reconstruction model...