Geoff Dyer at Literary Hub:
And the title is not just a sonorous bit of rhetoric plucked from Shakespeare by producer Elliott Kastner, who needed something better than the “awful fucking title” MacLean had come up with (Castle of Eagles). Kastner’s title cleverly inverts or, as is said in the world of agents and double agents, “turns” the intended sense of the lines in Richard III: “The world is grown so bad / That wrens make prey where eagles dare not perch,” words that Burton could have enunciated with the clarity Larry Olivier would later bring to the voice-over of all twenty-six episodes of The World at War, starting with the famous opening shots of Oradour-sur-Glane (“Down this road, on a summer day in 1944, the soldiers came . . .”), a clarity Eastwood neither attempts nor envies, especially since the English officers in the briefing all look like they’re kitted out in uniforms from the previous war or a shelved episode of Dad’s Army while he lounges at the back in something much sharper, more contemporary, more American-looking, sporting a post-Elvis haircut and wearing the shoulder flashes, as Wymark points out, of the American Ranger Division.