 Complete the following phrase:  Vietnamese over history have displayed immense ingenuity in spite of not sharing a language with its northern neighbor whose imperial examination system produced a scholar-bureaucrat class of scientific researchers and publications. Historically Vietnamese innovation has been best demonstrated during wartime, in which Vietnamese developed on top of native, Chinese, Western and other inventions and military tactics. Brave Vietnamese military leaders and warriors developed practical wartime strategies and technology to deal with Chinese intruders, for example at Battle of Bạch Đằng in 981 when Ngô Quyền developed an original technique of sinking Chinese navy fleets. The same original technique of sinking naval fleets developed by Ngô Quyền was later employed by Vietnamese generals to repulse 