Mark Harmon stars as Special Agent Leroy Jethro Gibbs on...

Mark Harmon stars as Special Agent Leroy Jethro Gibbs on "NCIS." Credit: CBS / Cliff Lipson

The 300th episode of “NCIS” on Tuesday night was officially labeled “Season 13, Episode 18 . . .” No big deal. No fanfare. There were some stories in major media outlets that did announce the arrival, while parsing, as usual, the eternal mystery: How did this show get this far? But the easy answer was for all to see, or the 16 or so million who tune in every Tuesday. They don’t need answers. They already know.

Nevertheless, the endurance of “NCIS” is in fact remarkable and anomalous. Not only TV’s most-viewed drama, “NCIS” is one of primetime’s most abiding, reaching a milestone only a handful of dramas — like “ER,” “Law & Order,” “Gunsmoke,” “Bonanza” — ever reach. Typically, successful shows last around seven seasons, the extent of the average actor contract, but “NCIS” has nearly doubled that life span. The show may have aired its 300th episode Tuesday, but will wrap its 13th season this May. There’s no end in sight. Leroy Jethro Gibbs — Mark Harmon — will be back for a 14th. The 400th episode should arrive sometime during the 19th season, when the silver fox is just a little more silver.

Tuesday’s 300th, titled “Scope” — about a former combat sniper, Marine Gunnery Sergeant Aaron Davis (Taye Diggs), wounded in battle, suffering from PTSD, and whose rifle was stolen by a mercenary intent on destabilizing the world economy — was consistent with the spirit of the preceding 299. Deeply and unapologetically patriotic (Tuesday’s episode had parallels to one of the biggest movies of the past two years, “American Sniper”), “NCIS” is the one show fans know they can turn to without having their worldview challenged, their soldiers maligned, their country scorned, or their heroes disparaged. “NCIS” is, always has been, dismissed as the show for the silent majority, coddling them with flag-waving and TV archetypes and antecedents that reach all the way back to the Precambrian era of television. All this has made TV’s biggest drama not only unfashionable but a Hollywood outlier, with just three Emmy nominations over all these years. (Even GLAAD has nominated “NCIS” twice.)

But to dismiss “NCIS” — as critics and the Hollywood establishment have done for years — is to also dismiss its preoccupations, and those have been the preoccupations of much of the country over the same time span: Intractable, brutal foreign wars, national security, the war on terror and the grinding emotional and financial cost of these wars on soldiers and families. The toll may be out of sight, out of mind, for most Americans, but not to veterans — or to viewers of this show. “NCIS” makes certain of that. Easy to forget what that acronym stands for — Naval Criminal Investigative Service — but these issues really have been the narrative meat and potatoes for this meat-and-potatoes drama.

“NCIS” premiered Sept. 23, 2003, or four months after major combat operations ended in Iraq. Of course, they had just begun, with nearly 1,000 U.S. troop fatalities a year from 2004 to 2007. As a reminder that the war continues, “NCIS” revisited the subject of Iraq again Tuesday. Diggs’ character, suffering from a grievous wound, refused to allow his daughter to see him, and naturally it was left to Gibbs to heal the breach. There was a moving scene in the soldier’s car, as he studied the gun he was about to put to his head. Flashback to a moment of desperation for Jethro, too, when he held a cocked pistol to his head. (As fans know, Gibbs was a former Marine Corps sniper in the first Gulf War.)

“Where are you headed,” Jethro casually asks.

“I don’t know,” says Davis.

The scene featured a pair of old pros easily nailing their lines — there were only two, after all — but also capturing the emotional wallop of an important veterans’ issue in just under 30 seconds. That’s economic storytelling, also powerful television.

Gibbs ended the episode returning to his roots, in one of those cathartic acts that saved the day and maybe his own soul. Getting the bad guy in the sights of his sniper’s rifle, he makes one clean shot.

That’s the other secret to the show’s success. Thirteen years later, the wars in Iran and Afghanistan continue. But the war on “NCIS” ends before the last commercial break. NCIS Special agent Leroy Jethro Gibbs — the silver fox himself, hero to 16 million — makes certain of that.

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