[Note 1] The directors edited their footage to recreate a mission against an unidentified target in northern Italy that resembles that of a May 1, 1944, mission against a railroad tunnel at Rignano sull'Arno, Italy, in which Lt. Col. Gilbert O. Wymond Jr. was awarded the Silver Star for destroying an ammunition dump concealed in a house near Siena and incurred severe damage to his P-47, Hun Hunter XIV.

The film next brings the audience to Alto Air Base, Corsica, introducing us to members of the 65th Fighter Squadron and explains the objectives of Operation Strangle by way of an after-breakfast briefing that merges into an animated map of Italy showing the Allies stuck at the Gustav line, and the mission to cut off the supply lines by destroying bridges and roads in Northern Italy.

[Note 3] The film then follows the pilots led by their young squadron commander through the tense moments before the flight, identifies them by name as they take off in pairs, and observes their journey to the mainland while flying in formation.

Following the success of his documentary, Memphis Belle: A Story of a Flying Fortress, filmed in the first half of 1943, Wyler returned to Europe with a team consisting of Sturges and screenwriter Lester Koenig.

He arrived in Rome shortly after its liberation in June 1944, followed by the rest of the team a few days later, focusing on Operation Strangle at the suggestion of General Henry H. Arnold.

Maslowski was transferred to the 9th CCU and Wyler used its cameramen to try to complete the assignment, but the weather proved too poor for color photography and only more footage of damage on the ground was obtained.

[9] Wyler remained in Europe touring captured areas and in March 1945 decided to make one last flight in the B-25 to film more "atmosphere shots.

He had suffered total deafness as a result of nerve damage in the noisy unpressurized aircraft, and was returned to the United States on April 10, 1945 for hospitalization.

Before Thunderbolt could be edited, when the war in Europe ended, the project was shelved and Wyler found little interest, even in the AAF, for completing the film.

Recovering part of the hearing in his left ear, Wyler completed the film and attempted to drum up support for its release by showing it to Hollywood trade publications in October 1945.