The Real Reason Gibbs Named His Boat Rule 91 On NCIS

Many things have come and gone over the course of the 19 seasons of "NCIS" but one constant has been Leroy Jethro Gibbs (Mark Harmon) and his rules. Introduced in the very first episode of the series (not counting those backdoor pilot episodes on "JAG"), Gibbs' Rules are the NCIS supervisory agent's way of imparting his sage wisdom on those around him.

One rule, in particular, played a prominent role both in the Season 18 finale and the recent Season 19 premiere. That would be Rule 91, which was both the title of the season-ender and the name Gibbs used to christen his latest boat. But what exactly is Rule 91 and what does it mean in the grand scheme of things?

As Gibbs declares in the final episode of Season 18, Rule 91 states, "When you decide to walk away, don't look back." This makes his choice to use the rule as his boat's name fairly self-explanatory. Gibbs had been kicked off the force and was using the Rule 91 to conduct his own off-the-books investigation into a serial killer during the finale, implying that he was in the process of leaving his old life for good. But when his boat exploded in the final moments of the episode, it gave the vessel's name a deeper and more meta meaning.

The "NCIS" Season 19 premiere episode, "Blood in the Water," sees Gibbs surviving the explosion of the Rule 91 and eventually reuniting with some of his former NCIS team members, including McGee (Timothy McGee). They are on the shores of the lake where Gibbs washed up investigating the same serial killer.

While McGee is relieved to see that Gibbs is still alive, he does have some opinions to share about Rule 91, both as a boat name and a concept. "Rule 91 sucks ..." McGee explains. "Because it is in direct violation of Rule Number 1: 'Never screw over your partner.'"

But Gibbs is still well within the parameters of his own rules. As he explains to McGee, now that he's been kicked off the team, nobody from NCIS counts as his partner. However, the change in circumstances has also led to a change in Gibbs' plans and it now appears that he's amenable to working with his former NCIS colleagues to track down the killer.

This back-and-forth mirrors Harmon's own supposed relationship with "NCIS." Early in 2021, rumors were swirling that Harmon was planning his own exit from the show. Allegedly, he agreed to come back in a limited capacity when he learned that if he didn't return for Season 19, the show would simply be canceled (via The Hollywood Reporter).

So, in real life and on the series, it looks like Rule 91 has been both literally and metaphorically blown up. Still, even though he's back for now, don't be surprised if Gibbs/Harmon calls on Rule 11 when the hunt for this serial killer comes to an end: "When the job is done, walk away."