The Scottish actor plays Dr. Owen Hunt, a former U.S. Army trauma surgeon who served in war-torn Iraq.
He admits he has been bombarded with fan mail from veterans of the current conflicts in Iraq and Afghanistan, who are pleased to see the difficult subject of post-war trauma dealt with on primetime TV.
McKidd says, "We have had a lot of letters from people who are grateful that a show of this size and reach is dealing with a subject like this. What's going on over there (in Iraq and Afghanistan) is very controversial politically, but we've been trying to tell the human story out there.
"We're telling the story of these brave men and women and what it is to come back, pick up your life and move forward with that experience of a war zone. There's been a lot of positive feedback from veterans. They are delighted we are casting light on a subject that not many people are talking about."
And McKidd is "proud and pleased" that he is able to make a small contribution, adding: "It's great to know that people are not just watching, but taking something from it."