The crude gun that Kirk builds from a bamboo tube, home-made gunpowder and diamonds to defeat the Gorn captain on the planetoid chosen by the Metrons.
The bamboo cannon is the makeshift weapon assembled by James Kirk in the original series episode Arena. The Metrons have placed him and the captain of a Gorn ship on a barren world to settle their conflict in single combat, promising that the materials for a weapon are present.
The Gorn is far stronger and shrugs off thrown rocks. Kirk notices deposits of sulphur, potassium nitrate and coal, and large rough diamonds lying on the ground. He packs a length of thick bamboo with the mixture, loads the diamonds as shot and lights it with a spark.
The blast fells the Gorn. Kirk then refuses to kill his helpless opponent, and the Metrons, impressed by this mercy, release both ships.