Re: Cockpit of the Enola Gay
Not sure whether they were sitting on them but the backrests on those seats do appear to be "hollowed out" for a back parachute.
In any case, the pilot's seat did once have a cushion on it. It was put there by Gen. Paul Tibbets (USAF, ret.), who sometimes would drop by and was allowed to sit at his old station. That cushion reportedly was the only item on the airplane that wasn't exactly as it was on 6 Aug., 1945. I guess they removed it on the occasion of his death.