There was some initial confusion on the way to refer to the new military campaign in Afghanistan. With the end of the ISAF mission - and President Obama saying that our war in Afghanistan had come to a 'responsible' end - we needed a name to replace "Operation Enduring Freedom". Just like we needed a new name in Iraq once we had won the war there - "Operation Iraqi Freedom" became "Operation New Dawn"; which, by the way - because the war wasn't really over in Iraq either, is now called "Operation Inherent Resolve".
So, back to the apostrophe . . . seems the Department of Defense has an apostrophe . . . and ISAF didn't. I was perplexed and didn't know how to type the phrase. So I went both ways; which in today's Army is now perfectly acceptable . . . I have been told - no first hand experience. But now, the word is out. Use the apostrophe. That makes it a real pain in the neck but I will struggle with it. It is now "Operation Freedom's Sentinel". And, just to clear away any confusion - "Operation Resolute Support" is the NATO term and "Operation Freedom's Sentinel" is the U.S. term.
Read more in "Amid Confusion, DoD Names New Mission 'Operation Freedom's Sentinel", Military.com, December 29, 2014.