The Hindenburg

May, 1937. Kathie Rauch from Milwaukee, Wisconsin sends a letter to the German Embassy in Washington, D.C. claiming the Hindenburg zeppelin will explode after flying over New York. In the meantime, Luftwaffe Colonel Franz Ritter (George C. Scott) boards with the intention of protecting the Hindenburg as various threats have been made to down the airship, which some see as a symbol of Nazi Germany.Ritter is assisted by a Nazi government official, SS/Gestapo Hauptsturmführer Martin Vogel (Roy Thinnes), who poses as official photographer. However, both operate independently in investigating the background of all passengers and crew on the voyage. Ritter has reason to suspect everyone, even his old friend and former mistress, Countess Ursula von Reugen (Anne Bancroft), who vehemently opposes the Nazi regime.Other prime suspects include card sharks Emilio Pajetta (Burgess Meredith) and Major Napier (Rene Auberjonois), Edward Douglas (Gig Young), a suspicious German-American ad executive, as well as several crew members and even the Hindenburg captains Pruss (Charles Durning) and Lehmann (Richard A. Dysart).As the Hindenburg makes its way to Lakehurst Air Field, events conspire against Ritter and Vogel. They soon suspect the rigger Karl Boerth (William Atherton), a former Hitler Youth leader who has become disillusioned with the Nazis. Ritter attempts to arrest him. Boerth resists. He requests help from Ritter, whose son was killed a year before. Boerth's girlfriend, Freda Halle, was killed while trying to escape arrest as the Hindenburg crossed the Atlantic. Boerth, upon hearing the news of Halle's death, plans to commit suicide by staying aboard the airship as the bomb goes off.Ritter eventually agrees with Boerth to set the bomb to detonate at 7:30 p.m., when the airship should have landed and passengers disembarked. While setting up the bomb (a small C-4 plastic explosive), Boerth drops a knife, which was later revealed to have been stolen from Rigger Ludwig Knorr. Vogel starts to work behind Ritter's back, arresting Boerth and confiscating the Countess's passport.As the airship approaches Lakehurst Naval Air Station at 7:00, Ritter now realizes the landing has been delayed and searches for Boerth to ask where the bomb is. Vogel is caught by Ritter torturing Boerth and gets into a fight with Ritter and is knocked unconscious. An injured Boerth tells Ritter the bomb is in the repair patch of gas cell 4. Ritter attempts to defuse the bomb, but is unable to do so in time and is spotted at the last few seconds by a now awakened Vogel. The bomb explodes, killing Ritter instantly and sending Vogel flying down the walkway. Vogel survives, being carried by ground crewmen, while Boerth dies of his burns.At this point the film changes to monochrome in order to match up with the actual newsreel footage of the disaster. Passengers and crew struggle to survive the fire. The disaster scene ends when the camera pans over wreckage, towards a strip of burning fabric that says "Hindenburg" on it. The following day, with the fire cleared, a list of passengers who died or survived is described briefly, while the wreckage is examined for the inquiry before being cleaned up.The film ends with a tribute to Herbert Morrison's radio commentary, with the memorable quotation, "Oh the humanity," as the Hindenburg flies once again, only to disappear again in the clouds.

Question: What was the bomb made of?
Answer: C4