I am reading "The Buccaneer Boys" at the moment and the story by David Whilby mentions this. Buccaneer crews were cleared down to 100 feet and the pilot had to warn the navigator to look ahead if he was going to look inside the cockpit. He mentions a crew at Nellis nearly went in when they forgot this, and it was only them striking a telegraph wire at 37 feet which got their attention and saved them from disaster. As an aside, it seems everybody had bags of fun flying the Buccaneer.