Major Penney is one of 2 USAF F-16 pilots who was given orders on a fateful day back in September 2001 to bring down a certain United Airlines flight 93 by whatever means necessary.
Stationed at Andrews Air Force Base, she and Col. Marc Sasseville were the first to respond to ensure flight 93 did not reach Washington DC airspace. They had just come from training in Nevada and both planes were still loaded with dummy rounds. Due to the chaotic nature of the day, there was no time to actually arm the F-16s with live ammo. They knew they would have to ram the airliner with their own jets.
Fortunately for them, the passengers in Flight 93 took matters into their own hands and the plane went down in a field in Pennsylvania.
I think most people (I know I did), no matter which branch of the military, get a quick pang in the chest when they raise their right hand and repeat that oath - suddenly realizing that maybe they just might be called on to do exactly what Maj. Penney & Col. Sasseville almost had to do. When you swear to support and defend the Constitution of US against all enemies, foreign and domestic - it could possibly mean sacrificing yourself for the good of others.