The report describes the Purpose, Procedure, and obtained Results of a mission to Bangkok (Thailand) undertaken on July 16-18, 2009. The main goal of the mission was to inspect the fire arms located in the Museum of Weaponry of the Ministry of Defense in order to identify the cannons produced by Joao da Cruz (1610?-1682), a half-Portuguese founder employed by the King of Cochinchina (Central Vietnam) and to take pictures of the inscriptions made by Joao on the cannons. When this part of the mission was accomplished, the investigator visited three more exhibitions of old weaponry located in Bangkok and discovered, in the National Museum, two more cannons most likely made by Joao in 1651 during his stay in Cambodia (identified by the Museum staff as “cannons of Spanish origin”). The results of the mission will be used in a forthcoming paper on the transfer of Western technological expertise into Vietnam in the late 17th- early 18th centuries.