I was watching an Army Air Corps film about the Memphis Belle the other night, and one thing struck me. The crew of the B-17 heavy bomber, on completing their 25th and final mission, were to be sent back to the United States to train new crews, because as the narrator claimed, "their experience was priceless." I can see how this would be the case for a lot of different jobs in the service: fighter pilots, tank drivers, and so on.
But for bomber crews, it seems a bit harder to see the importance of that experience. They're trained to fly in formation, and their main threats are anti-aircraft fire and enemy fighters. Whether AA hits you or not is more luck than anything else, particularly on the actual bombing run, and the main defense against interceptors was basically a herding, "safety in numbers" strategy. Experience seems in this situation to be of fairly marginal value, particularly for gunners: is a tail-gunner with 20 missions under his belt really more effective than one with 2 or 3?
But I don't want answers that just tell me some version of "Of course it's valuable!" or "None of us can really know what it's like!" I'd like to see data: were experienced crews actually more likely to carry out their mission and return home safely? Were crews on their first few missions more likely to be shot down?
Were crews on their first few missions more likely to be shot down?
That does seem to be the case. Courage and Air Warfare: The Allied Aircrew Experience in the Second World War by Mark K. Wells includes a table of percentage losses by mission number from a study of 2,085 combat airmen (data from Trend of Losses Related to Combat Crew Experience, Heavy Bomber Operations). Loss rates peaked on missions 2 (7.2%) and 5 (7.3%), and were lowest on missions 22 (0.9%) and 24 (0.5%). Wells says "... further analysis showed that crews were statistically most at risk during the first ten missions." The RAF's Operational Research Section reached similar conclusions, Randall Wakelam's thesis Operational Research in RAF Bomber Command, 1941-1945 quotes from ORS S 187 The Effect of Experience on Operational Efficiency based on 17,000 sorties: "the investigation confirms the higher missing rate, crash rate, early return rate and combat rate among inexperienced crews". There was also a slight increase in losses around the middle of a tour, attributed to "over-confidence and consequent lack of care". As you say, an individual gunner would in all probability have a lower impact on survivability than a pilot, but I'm not aware of a breakdown of the effect of experience of specific crew members, it would be hard to measure statistically as crew generally operated as complete units.
In addition to loss rates other considerations were the accuracy and effectiveness of bombing. Another ORS report showed that "almost invariably" the least accurate attacks were made by crew who had flown fewer than three missions, and interviews confirmed that pilots were "completely taxed" around the target area on their first two missions.
Publicity would emphasise the invaluable experience of the crew rotating out to training units, and indeed the importance of using combat-experienced crew in training was stressed by e.g. General "Hap" Arnold, but relief from combat fatigue was at least as important a factor in rotation. John Terraine in The Right of the Line calls the tour of operations with promise of non-combat operations afterwards "a sheet anchor of morale in Bomber Command" that "made the unbelievable endurable". A similar point is made in Combat Crew Rotation by the Historical Studies Branch of the USAF Historical Division.