War II. Vonnegut’s experiences were exceptional in the scale of destruction he observed and experienced. Vonnegut was a survivor, ironically while a prisoner of war, of the Allied firebombing of the German city of Dresden. The author suggests that this was similarly as horrific as the atomic bombings of Hiroshima and Nagasaki. In his opening chapter, Vonnegut describes a conversation he had with his publisher, during which he found himself obligated to explain the logic of having written a book about the bombing of Dresden. As Vonnegut summarizes his response to the uncomprehending publisher,

It is so short and jumbled and jangled, Sam, because there is nothing intelligent to say about a massacre.

When considering the scene in Chapter 4 of Slaughterhouse-Five when the novel’s protagonist is viewing a film about the Dresden air raid, it is rather important to keep in mind the surrealistic nature of this book. Writing Slaughterhouse Five was a cathartic experience for Vonnegut. It also illuminated the incomprehensible nature of the historical context at the center of the story: World War II and the slaughter of tens of millions of people.

To understand the film-watching scene, then, it helps to remember the opening passage of Chapter 2, the real beginning of the story: “Listen: Billy Pilgrim has come unstuck in time.” Vonnegut’s main character spends the entirety of the story moving back and forth in time, often in the company of extraterrestrials who have taken the liberty of kidnapping the hapless individual. Throughout the novel the author includes continued reflections on the devastation he witnessed. That a film about the event that caused the devastation of the firebombing raid by Allied bombers should be viewed in reverse is only natural to the frame of the story. The author and his character are trying desperately to understand the scale of carnage, especially of an event largely unknown in the United States.

In addition, the role of film in establishing the fiction of war as a noble enterprise recurs throughout the novel. It begins in the opening chapter during Vonnegut’s discussion about writing the book with an old fellow veteran and the latter’s cynical wife. It is the wife, Mary, who objects to Vonnegut’s intrusion into her home for the purpose of resurrecting painful memories from the past:

“You were just babies in the war-like the ones upstairs!” I nodded that this was true. We had been foolish virgins in the war, right at the end of childhood. “But you're not going to write it that way, are you.” This wasn't a question. It was an accusation. “I-I don't know,” I said. “Well, I know,” she said. “You'll pretend you were men instead of babies, and you'll be played in the movies by Frank Sinatra and John Wayne or some of those other glamorous, war-loving, dirty old men. And war will look just wonderful, so we'll have a lot more of them. And they'll be fought by babies like the babies upstairs.” So then I understood. It was war that made her so angry. She didn't want her babies or anybody else's babies killed in wars. And she thought wars were partly encouraged by books and movies.

The film is viewed backwards because the entire process of writing Slaughterhouse-Five was an opportunity for the author to reflect on an event that existed beyond his comprehension. Vonnegut concludes this scene with the observation that, viewed in reverse, the horrific wounds suffered were reversed. As the bombers returned to their bases in England, he writes that “everything and everybody [was] as good as new.” Imagine, Vonnegut is saying, that the whole awful experience had never occurred.

All or at least most of Kurt Vonnegut's writing is pointedly anti-war. As a young man, he lived through the firebombing of Dresden, which shocked him to his core and is the reason why he mentions the event in many of his works, including this novel. Through satire and absurd, he criticizes the horrors and the brutality of war, especially today's war, which is capable of massive destruction thanks to new technologies and weapons.

Considering your question, I think that it's the new technologies of war that are particularly important. When Billy watches the war movie backwards, he sees anti-aircraft weapons sucking bullets out of planes and people; he sees the planes and bombs being shipped back into the factories where they were made, to be reassembled; he sees clever scientists dismantling all those tools of destruction, and he sees all the bad chemicals being buried back into the ground, where they can't hurt anyone ever again. There are many ways to interpret this backwards movie, but one of them is to view it as a symbol of our capabilities and choices.

In that way, the backwards movie shows us that we as human beings are capable of taking all of those dangerous objects and weapons and getting rid of them. Scientists around the world could dismantle all of them and dispose of the materials. We can't bury all of the materials, but we could stop using oil and uranium for destruction, at least. The human race has that knowledge and we have that capability, but we choose to fight each other. We could heal and help each other, but we make weapons. We could wipe out all weapons of mass destruction, but we make more. We have every chance to do good, but for some reason we keep making the wrong choices, and wars continue to rage around the world.

Even though the pictures in the movie are physically the same when played backwards and forwards, the narratives we attach to these pictures are different.

When played forwards, we decry the bombing.

When played forwards, we celebrate the return of things to the earth.

The order matters. It chages the value that we attach to the pictures.

Also, watching a war movie backwards changes the "story" of the movie, which would be a story of destruction, if watched in normal chronological order. As it is shown backwards, the movie shows chaos to creation. Rather than everything being destroyed, killed, and pulled apart, it is made whole and born anew.

The entire novel deconstructs linear time, and watching the movie backwards is an enactment of this. Watching the movie backwards triggers in his mind memories of WWII, here imagining it going back to the beginning of time.  This imaginative flight signifies the timelessness of war and perhaps, too, the repeated evidence that humankind is violent and cruel. Throughout the book Billy goes back in time or out of time, so to watch a movie backwards makes "sense" in this sort of logic.