frighten Americans out of their wits

やっと日本に帰れた万次郎は尋問攻めで何ヶ月も故郷の家に帰してもらえませんでした。
Manjiro drew a picture of the battlements he had seen in Boston Harber. "Even the small port of the town where I lived is fortified with guns," he said. "The shells are about ten inches in diameter. The guns measure some twelve feet. Ships are supplied with cannons, and the sailors armed with rifles. There is hardly any weapon that can frighten Americans out of their wits."
"frighten Americans out of their wits" の個所は慣用句の様です。単に「米国人を脅かす」と解釈しても間違いではないと思いますが辞書で調べてみます。
・Cambridge Idioms Dictionary: also scare somebody out of their wits: to cause extreme fear in someone Don't sneak up behind me like that - you frightened me out of my wits!
・Macmillan Dictionary: frighten/scare the wits out of someone or frighten/scare someone out of their wits: to make someone feel extremely frightened: The movie scared the wits out of us.
・Wiktionary: To frighten someone to such an extent that they behave irrationally: He scared me out of my wits, sneaking up behind me in the dark, like that.
なるほど単に脅かす程度ではないと言う事ですね。
その後万次郎は勝海舟が艦長の咸臨丸で米国に行った時は通訳として働いたのはもちろん、勝海舟を含め大半の日本人が船酔いで苦しんだので、万次郎が実質的に艦長の役目も果たしていた様だ。しかし、稀有な経験を経て、西洋の知識を身に付け、英語を解し有能な万次郎にもかかわらず、元が侍ではなかったために、ねたみもあり、明治政府の要職には就けなかったのは残念でした。