Not David Letterman, but Jonathan Letterman.
This is Ranger Barb Sanders of the Gettysburg National Military Park giving a 2016 winter lecture on how the innovations of Jonathan Letterman led to improvements in the Army Medical Corps from the Civil War to World War II.
The video’s description reads, “Education Specialist Barb Sanders explores advancements in military medicine from the end of the Civil War to World War II. From the system of triage, evacuation and hospital care instituted by Medical Director Jonathan Letterman, through both the First and Second World Wars, the medical advances of the Civil War ultimately resulted in the advent of penicillin, blood collection, aeromedical evacuation and the treatment of psychiatric casualties.”
As we’ve become accustomed to seeing from the rangers at Gettysburg, this is a wonderful presentation.