Apocalypse Now- 'what happened?'

(*spoiler alert)

Apocalyse Now is a film that details the entire journey of Captain Willard as he travels up the river to Cambodia during the Vietnam War to complete a top secret mission. The beginning and end are clear: Willard receives the assignment, he travels up the river and he completes the assignment. We understand that he must kill Colonel Kurtz, an American soldier, but everything that happens in between is completely chaotic. Willard and the four other men sharing the small boat stop along the way for various reasons. They ride a helicopter as it drops bombs on a small village, they stumble upon a group of soldiers who are acting without a leader, and they are nearly mauled by a tiger. In a particularly disturbing interruption, Willard’s boat comes alongside a small boat of Cambodians and the commander orders one of the soldiers to search it. Without warning, one soldier opens fire with a machine gun and another soldier follows his lead until they have shot each Cambodian passenger countless times. When this eruption of gunfire ends, suddenly the men, who ruthlessly killed the passengers, turn their concern to the only surviving woman. Their attention and their emotions switch illogically, and we are never given explanations before the soldiers continue on.
The film becomes progressively violent and odd, and by the end my only thought was, “What just happened?” I was not only confused and overwhelmed by the sequence of events but also disturbed by many of the gruesome images.
But the look on Willard’s face in the final shot indicated the same thought: “What just happened?”
“What did I see? And what did I do?”
His eyes stare forward without blinking and he controls the boat with mechanical motions. The island slowly drifts away in the background, but Willard’s expression never changes. A voice-over speaks the last words of the film, reflecting my feelings and the apparent numbness of Willard: “The horror.”