The show is loaded with in-jokes and callbacks

When Mark Harmon’s character Jethro Gibbs is shown in flashbacks, the actor portraying young Gibbs is Sean Harmon, Mark’s son.

Gibbs’ father, portrayed by Ralph Waite, is said to have been a fighter pilot in Wor8ld W8ar II—just like Harmon’s father, Tom Harmon.

The opening credits of some early seasons of the show contain footage of an aircraft carrier navigating the Golden Gate Bridge—which was shot for “The Presidio,” a 1988 military drama starring Mark Harmon. In another episode, Gibbs remarks that when he was younger, Ducky looked like “Ilya Kuryakin.

” For viewers not familiar with classic ’60s TV, Ilya Kuryakin is the name of a character played by Ducky’s current portrayer, David McCallum, on “The Man from U.N.C.L.E.”