The R.A.F. went after the Baltic port of Liibeck one night in March 1942 because Lübeck was a vital link on the Wehrmacht supply line to Russia. It was no part of the R.A.F. plan that the fire bombs rained down on Lübeck's beautiful 13th Century Marienkirche, but fire melted the church's great bell, gutted the interior. Repair crews got a surprise: whitewash had peeled from the walls, revealing patches of vividly colored frescoes beneath.
Reinforcement of towers and masonry came first, but by last year trained workers began chipping away the rest of the Marienkirche's whitewash. Slowly they uncovered panel after...