Saddle Rash (2002)

S1E18 X Marks the Spot

During a trial for a lethal new missile named "Operation Powder Keg," the Air Force selects an "uninhabited island" that coincidentally turns out to be Gilligan's Island. When the missile strikes and fails to detonate, Gilligan is picked to crawl inside and disarm it, as he is the only one small enough to fit through the opening.