As a Cardiovascular surgeon, we use hypothermia routinely in our complex cases. Cooling the patient reduces the metabolic rate and demands for oxygen. We use moderate hypothermia, 25-30 degrees Celsius, to protect the heart during long and difficult cases. We use deep hypothermia, 13-16 degrees Celsius, when we have to completely shut off the heart-lung machine for a while to reconstruct the aorta at the point where it gives off the branches to the brain. At those temperatures, we can cease all circulation to the body and brain for about 30-45 minutes to get the work done. Much of the early work done on hypothermia in heart surgery was based on the cruel Nazi experiments done on cold water immersion on prisoners to predict Luftwaffe pilot survival in the North Sea.
Rarely, we can use the heart lung machine to warm someone up who has been brought in with severe hypothermia, not a common occurence here in Florida.
Only survival data I can find on WWII ditching was 38% survival for B-17 ditching and 27% survival for B-24's. A total of 4,361 8th AF crew ditched during the war, 1,538 survived, for an overall 35% chance of survival.