By By Eric Auchard VIENNA (Reuters) - Three Israeli defense contractors behind the Iron Dome missile shield and related systems were robbed of hundreds of documents by ******s linked to the Chinese government starting in 2011, a U.S.-based computer forensics expert said on Tuesday. Comment Crew, as the hacking group is k**wn, stole designs for Israeli rocket systems in a spree of attacks during 2011 and 2012, Joseph Drissel, chief executive of Cyber Engineering Services (CyberESI), said in a phone interview. The targets of the online attacks were top military contractors Elisra Group,*Israel Aerospace Industries[ISRAI.UL],*and*Rafael Advanced Defense Systems. The companies built the system that **w partially insulates Israel from rocket barrages fired from the Gaza Strip.