Saw this story elsewhere and found it fascinating
https://www.warhistoryonline.com/war-articles/abraham-wald.html
People tell a similar story about the British Operational Research Unit. I'm not completely convinced about some of the details. For example, as a rule, even quite late in the war, bombers didn't carry much armour. Armour is heavy and each pound of armour is a pound less of bombs or fuel. The fewer bombs you can carry, the more planes you need which risks more people's lives.
In fact the ORU discovered that by far the most important variable in determining whether a bomber was shot down or not was the amount of time spent flying over enemy territory. Thus they proposed that the RAF night bombers should be stripped of their guns. This would mean the bombers could fly faster and higher with the same bomb load and also that, if the plane was shot down, two fewer people would be lost.
There's also a nice survivorship bias story about the introduction of helmets in the First World War. In 1914, the British Army used cloth caps for head gear. In 1915 they started introducing steel helmets. They were shocked to find out, after this, that the field hospitals saw a significant rise in head injuries. Apparently there were letters to the Times and such, but the explanation was simple. The people with head injuries would have been dead if they hadn't been wearing a helmet and would not have gone near the field hospital.
