I am not 100% positive about this, but I read somewhere that the 8th Air Force (the USAAF group that flew daylight missions over Germany out of bases in the UK) had the highest mortality rate of any US forces in WWII.Those lads were brave, the odds of completing 25 missions were not good.
"In 1942, during the first three months of America’s combat flights over Europe the average bomber crew was expected to complete 8-12 missions before being shot down or disabled. This in mind, the US Army Air Force decided that 25 missions while serving in a heavy bomber of the 8th Army Air Force would constitute a “completed tour of duty” because of the “physical and mental strain on the crew."
About 30 years ago I worked with a guy who was a captain and flew B-24 missions out of North Africa to the German oil fields in Ploiesti, Romania. He said that they partied pretty hard when they returned from missions!
If this subject is of interest to you I suggest that you read Joseph Heller's fictional / satyrical account of B-25 crews who flew out of Italy. It is a great piece of work and my B-24 pilot friend said that, in his opinion, it captured the essence of what he experienced during the war.