Each of the casemates in the Longues battery was built out of 600 sq metres of concrete and 4 tons of steel reinforcement. To withstand heavy bombing by Allied aircraft, the walls were nearly two metres thick. In addition, to avoid the casemates tipping over during bombing raids the German engineers designed an underground concrete flange which stabilised the bunker by preventing shells and bombs from exploding underneath it. This system of stepped concrete foundations proved particularly effective at Longues when 1000kg bomb exploded, completely ripping away the earth around the casemate but without actually tipping it over. This kind of concrete foundation was used for all naval batteries and worked extremely well. Experts have since corroborated this near invulnerability to aerial bombardment except in the rare event of the protective canopy being hit twice in the same place before the concrete was completely dry. Longues was not affected by the hurried construction in the last months leading up to the invasion building started in September 1943 and the battery was almost complete in June 1944.
In this diagram you can see that the Army casemate had no underground concrete flange which made them Susceptible to tipping over when bombarded.
It was a different story, however at Houlgate, where a 406mm armoured shell fired from a ship anchored 22 km (14 miles) off the coast passed clean thru a casemate. However on closer inspection the third casemate at Longues can seem to have been hit on the right side by a 1000kg bomb which has pierced the canopy. None of the gunners were killed by the falling masonry and in fact it has been proved to have crumbled because of a poor quality concrete mix. Perhaps this was an act of sabotage by a French conscript working for the Todt Organisation.
Longues Battery is the only one in the region to have kept its guns, as you can see in this picture.