Plot

The castaways form a military unit led by Mr. Howell when an unidentified enemy begins attacking them with hand grenades.

Sitting reflectively against a rock, the Skipper (Alan Hale Jr) sighs and writes out "steak" in the sand as Gilligan (Bob Denver) comes up and asks how he liked his steaks. At that moment, an object resembling an avocado flies over their heads. The Skipper recognizes it as a hand grenade just before it explodes. Collecting the fragments of it, the Skipper shows them to the Professor (Russell Johnson) and Mr. Howell (Jim Backus), who dismiss their plan of action. They decide on surrendering with a white flag, but they've already turned the idea down by time Gilligan comes back with one. Before they can come up with another plan, another grenade flies overhead and explodes near them in the compound. Taking charge, Mr. Howell proclaims himself General and makes the Skipper Secretary of the Navy and the Professor Chief of Intelligence, but they just humor him along as they search the Island. Gilligan, however, gets stuck by a pin when Mr. Howell dives under the table from the grenade and is sent to the girls to treat his wound when Mrs. Howell (Natalie Schafer) and Mary Ann (Dawn Wells) exit, Ginger (Tina Louise) entertains Gilligan by singing It Had to Be You as he lays down and smiles. They over-eagerly wrap up his entire arm, and Gilligan rejoins the men scouting the Island. They're then surprised by gunfire and take cover, but their shooter takes off, abandoning the submachine gun. While they're wondering why their attacker left the gun, Gilligan notices a gorilla (Janos Prohaska) come out of the woods and throw a grenade at them. They take cover again as the ape takes off again into the jungle. The Professor deduces that the gorilla watched men fighting with the weapons during World War Two and is now imitating what it saw. Tracking it to a cave, they realize where the weapons have been coming from. Their plan to sneak the weapon boxes out fails when the gorilla catches them in the act and chases them out of the cave. The Professor then realizes that the gorilla might be stared into immobility, but Gilligan flinches first and the gorilla catches him. Fleeing the cave, the men are trying to decide how to rescue Gilligan when they hear explosions. In the lagoon, Gilligan has taught the ape to throw the grenades across it where they harmlessly explode. After they're all gone, the only thing left is a strange red disc. The Professor tries stopping them, but it flies off and detonates, creating a huge mushroom cloud beyond the island as the professor relaxes that it wasn't a grenade. A few moments later, Mr. Howell is awarding Gilligan for his bravery when the gorilla returns. Everyone scatters except Gilligan as it reaches down and throws Mary Ann's pie saved for Gilligan into his face. Meanwhile, Gilligan just realizes that the gorilla's aim has improved.