. "Operation Alberich" . "organized retreat" . . . "Pursuit to the Hindenburg Line" . "organized withdrawal" . "Germans retreated to the Hindenburg Line" . "withdrawing to the Hindenburg Line" . "German withdrawal" . . . . "undertook a planned" . . . . . . . "began retreating to the line" . . "German withdrawal to the Hindenburg Line" . "German success" . . . . "United Kingdom" . . . "withdrawal" . . . . . . "1917-03-20" . . "German Retreat to the Hindenburg Line" . "German retreat to the Hindenburg Line 1917" . . . "Operation Alberich" . . "German retreat to the Hindenburg Line" . . .