WW1: Apologies if mentioned before. It was RFC/RAF policy until September 16th 1918 to ban parachutes. One wonders how many lives were lost thanks to that ridiculous order!
WW2: Survival rates from Lancasters were 15% and Halifax 25%, USAAF 50%. Freeman Dyson discovered that the escape hatch on Lancs was literally one inch too small to allow an airman to escape (with ease) with full gear and chute. He campaigned unsuccessfully to have it enlarged. He also computed that a Lanc minus two turrets and two crew members would have been 50mph faster. Again he was ignored.