marines

tell that to the marines (or the horse marines) a scornful expression of incredulity.

☞ This saying may have originated in a remark made by Charles II, recommending that unlikely tales should be referred to sailors who, from their knowledge of distant places, might be the people best qualified to judge their truthfulness. Horse marines, dating from the early 19th century, were an imaginary cavalry corps, soldiers mounted on horseback on board ship being a humorous image of ineptitude or of people out of their natural element. In 1823 Byron noted that That will do for the marines, but the sailors won't believe it was an 'old saying', and the following year Walter Scott used Tell that to the marines-the sailors won't believe it! in his novel Redgauntlet.

2003Peter LoveseyHouse Sitter So the official line was that the murders of Emma Tysoe and Axel Summers were unrelated. Tell that to the marines, he thought.