Last night I found an article on the Battle of Okehazama. It is general, but mentions historian Fujimoto Masayuki and Ota Gyuichi's Shincho-Ko ki. The article mentions Fujimoto's theory that Nobunaga did not use a surprise attack because it was not written in the Shincho-Ko ki. The Shincho-Ko ki is not perfect and does have some errors. My opinion on Nobunaga's tactic at the Battle of Okehazama, frontal surprise attack.