引用・参考文献 https://www.quora.com/Why-did-the-British-not-have-ventral-machine-guns-on-their-bombers-Other-nations-started-the-war-with-ventral-weapons-yet-beside-isolated-cases-like-the-Hampden-the-British-had-no-protection-and-lost-many-planes-andhttps://www.quora.com/Why-did-the-WW2-Lancaster-bomber-not-to-have-any-guns-on-the-underside
http://www.nicovideo.jp/watch/sm44902403
