NCIS has celebrated another milestone, and it's quite the feat: its 450th episode, in its 20th season.

Unlike the previous milestone hour, the 400th as part of Season 18, which revealed how Gibbs (Mark Harmon) and Ducky (David McCallum) met and included returns from Mark's son Sean Harmon and Adam Campbell to play their younger selves in the flashbacks, this time it was pretty much business as usual.

Below, we're taking a look at all the milestones 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.