Recently watched a documentary about the Mosquito raid on the prison at Amiens - 487 Sqn RNZAF lead the raid. In an interview one of the pilots remarked that he descended to 'about 10 or 12 ft above the ground' during the run-in to the target, but 'I was a bit uncomfortable about going any lower'
...and he was doing that from chinagraph marks on the windscreen! High-tech indeed!