When did NCIS Los Angeles first appear?

It is the 22nd and 23rd episodes of the sixth season.

Season 6, Episode 22: Legend: Part 1

Original Air Date—28 April 2009

A murdered Marine is linked to a possible arms deal. Leading Gibbs and McGee to go to Los Angeles to work with NCIS OSP, while Tony and Ziva work the case from DC.

Next US airings:

Wed. Nov. 11 8:00 PM USA

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Season 6, Episode 23: Legend: Part 2

Original Air Date—5 May 2009

Gibbs and McGee continue working with NCIS OSP to find out what the cell plans on doing with the weapons they're trying to purchase. But a foreign agent has different plans.

Next US airings:

Wed. Nov. 11 9:00 PM USA