Chinese Ships Harass US Survey Ship

The Pentagon released tapes this past week from a US Survey ship on March 8.  On the tape a Chinese vessel was aggressively harassing the US ship, with an unarmed and mostly civilian crew, because they believed the Navy was violating Chinese and International law.  

Would the Chinese vessel have gone further than 'harassment'  if they thought the ship had weapons?  Why wast the vessel trying to take sonar equipment from the survey ship?  I think there is more to this story than what both governments are releasing.  

www.cnn.com/2009/WORLD/asiapcf/03/20/us.china.navy/index.html