President Kennedy’s brother was killed helping Britain before Dec. 1941.
On August 12 1944, Joseph P. Kennedy Jr. was killed when his plane, packed with explosives for a top-secret bombing raid, exploded over southeast England.
You are right, the price for relying of very old memories. His service was from England (I presume in US aircraft). See detailed link below.
https://www.nps.gov/articles/000/joseph-patrick-kennedy-jr-a-dream-unfulfilled.htm
After reading about his deadly mission here, and looking at what happened subsequently to the Kennedy men who were politically active, I find myself wondering if the premature explosion might have been planned. I have heard that their father who was serving diplomatically in England was not well liked by some powerful people.