By Ned Ehrbar, CBS News

NEW YORK (CBSNEWS.COM) NCIS” is celebrating a milestone very few television series have reached: 300 episodes.

Details of the episode, titled “Scope,” have been kept understandably quiet ahead of Tuesday’s premiere, but series star Mark Harmon has promised the outing will not disappoint.

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We do at least know that the episode will feature guest star Taye Diggs as a Marine suffering from PTSD who factors into the teams investigation.

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“For our 300th episode, we needed a guest actor who could proudly portray one of our nation’s wounded warriors as well as participate in a very touching musical performance,”executive producer Gary Glasberg said in a statement. “This emotionally charged role is tailor-made for Taye Diggs, and we are so thrilled and honored to have him join us.”

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