#1338: in 1942 everyone in Britain was asked to send in photos they'd taken on holiday in northern France. they collected more than ten million, and used them as recon and scrutinised over the details. officers and infantry used them to orient themselves before they dropped. but they weren't very helpful at first: they could be misleading, especially because most were over 20 years old and people didn't tend to take holiday pics of military bases. for the D-day preparations, they used Combined Ops Assault Pilotage Parties - secret divers who'd go in on tiny submarines in the winter of 1943/44 and pop their heads up to survey the shore at night. in combination, they had a pretty good idea of the five beaches as they went in. shortly before the landings themselves, the first people to approach France were "frogmen" - Landing Craft Obstacle Clearance Units (LCOCUs, pron. "lock-youse") swam in advance and manually disarmed underwater obstacles: about 2,500. the defenses the frogmen had to disarm were very elaborate: far out, there were "belgian gates" (basically huge hidden fences), then logs pointing out to sea with mines on top so spike incoming craft. then a bit shallower, a row of ramps sloping upwards to capsize boats, and finally a row of "Czech Hedgehogs" (anti-tank defenses that look like those jumping jack things you roll).