'NCIS' 400th Episode: Where Does It Rank Against the Previous Milestones?

Jace Downs/CBS; Sonja Flemming/CBS; Richard Cartwright/CBS

NCIS has celebrated another milestone in its 18th season, and it's quite the feat: its 400th episode.

The hour revealed how Gibbs (Mark Harmon) and Ducky (David McCallum) met, and fans were treated to returns from Mark's son Sean Harmon and Adam Campbell to play their younger selves in the flashbacks.

10 Heartbreaking & Powerful 'NCIS' Episodes That Left an ImpressionSee Also

10 Heartbreaking & Powerful 'NCIS' Episodes That Left an Impression

We take a look back, from the heartbreaking (Kate's death) to the powerful (Taye Diggs' guest spot).

In honor of that milestone, we're taking a look at all the ones the procedural has marked so far. They've brought a team member on officially, introduced an agent's relative after years of only hearing about him, featured memorable cases, and been among the best episodes of the series. Scroll down to see our ranking, from least to most memorable.

NCIS, Tuesdays, 8/7c, CBS

NCIS Milestone Episode 50 Silver War
CBS

Episode 50: "Silver War" (Season 3, Episode 4)

This was the episode in which Ziva (Cote de Pablo) officially joined the team as its Mossad liaison, but other than that, there was simply not much memorable about it. (Then again, Episode 50, when 400 has aired, isn’t that significant of a milestone.)

NCIS Milestone Episode 250 Dressed to Kill
Richard Cartwright/CBS

Episode 250: "Dressed to Kill" (Season 11, Episode 16)

NCIS delved into the DiNozzo family in the second milestone episode to feature Robert Wagner as Tony’s (Michael Weatherly) father. Once again, Senior got wrapped up in the case (as he tends to do when he shows up), but for a milestone hour, that wasn’t all that special, either. Overall, it was as entertaining as any Senior episode, but it doesn’t hold up against the rest of the milestones.

NCIS Milestone Episode 350 Sight Unseen
Patrick McElhenney/CBS

Episode 350: "Sight Unseen" (Season 15, Episode 20)

This milestone saw the team, specifically Torres (Wilmer Valderrama), work with a key blind witness, Annie Barth (Marilee Talkington), to solve a case involving assault. It was seeing those two together that made this episode one to rewatch, as he came to understand just how much of an asset she was.

NCIS Milestone Episode 100 Chimera
Randy Tepper/CBS

Episode 100: "Chimera" (Season 5, Episode 6)

Gibbs and the team left behind the comfort of the office (and land) to investigate on board a top-secret naval research ship, and fans were treated to jump moments, singing from Tony, and an entertaining case.

NCIS Milestone Episode 150 Flesh and Blood
Sonja Flemming/CBS

Episode 150: "Flesh and Blood" (Season 7, Episode 12)

It only took 150 episodes, but fans finally met Senior in this milestone and got to see Tony’s relationship with his father after only hearing about it for years. It didn’t disappoint, and it would serve as the blueprint for DiNozzo episodes to come.

Mark Harmon Gibbs David McCallum Ducky NCIS Episode 400
Sonja Flemming/CBS

Episode 400: "Everything Starts Somewhere" (Season 18, Episode 2)

It only took 400 episodes, but we finally got to see the first case to bring Gibbs and Ducky together. Was it a memorable investigation? No. But the focus on their relationship, from those early days to present-day, made it very much a highlight of the series and the actors in both timelines work so well together.

NCIS Milestone Episode 200 Life Before His Eyes
Richard Foreman/CBS

Episode 200: "Life Before His Eyes" (Season 9, Episode 14)

The episode’s concept — asking “what if?” — wasn’t a novel one, but it worked quite well. What if Kate (Sasha Alexander) didn’t die? What if Gibbs didn’t kill Pedro Hernandez? What if his wife Shannon (Darby Stanchfield) and daughter Kelly hadn’t been killed (by Pedro)? Those are questions most fans have probably asked time and time again, and it turned out that for some, heartbreak was just inevitable, no matter what ultimately happened.

NCIS Milestone Episode 300 Scope
Jace Downs/CBS

Episode 300: "Scope" (Season 13, Episode 18)

One of the best episodes of the series, the 300th was pretty perfect. Gibbs connected with Taye Diggs’ Aaron Davis at Water Reed, suffering from PTSS; Davis eventually talked about the attack and provided necessary information to help the team solve their case. But it was the more personal moments — between Gibbs and Davis, the rest of the team as they headed to dinner, and McGee (Sean Murray) as he planned to propose to Delilah (Margo Harshman) — and a powerful rendition of “Hallelujah” (from Diggs) to cap it all off that puts this one at the top of the list.