The pivotal gruesome scene involved Snowden the gunner who was hit by flak.
Everything in that episode happened just as Heller reported it. The aircraft was hit by flak. The co-pilot panicked and ripped control of the ship from the pilot sending it into a steep dive. Heller in the bombardier's compartment was plastered to the roof of the 'greenhouse' in the nose and his intercom cable pulled out of the jack. When he jacked back in the pilot was yelling, "Somebody help the bombardier!"
When they got it strait that the call for help came from the rear of the plane, Heller was sent to the rear to help. He found the gunner Carl Frankel with a massive wound in his leg. Heller gave him a shot of morphine, packed the wound with sulfa and bandaged it. He stayed with Frankel until they got back to Corsica.
Unlike the novel, the gunner did not die and have his guts spill out on the floor.
See my essay here for more detail:
http://dansetzer.us/heller_index.htm
What was the second gruesome scene you are referring to? I am not recalling it from the movie.