RAF Spitfire pilots in WWII during the Battle of Britain. Life expectancy: perhaps 10 sorties.* Impact: "Never in the field of human conflict have so many, owed so much, to so few ..."
I rest my case.
(*One Google reference claims the life expectancy was 45 minutes of flight time.)
(Tom insists he is not old enough to have taken the picture of the Spitfire himself.—Erik)