The cited source (Wikipedia: First Strike (Nuclear Strategy), EntitySourceId 533045) discusses the concept across the article as a whole with no single dated origin given; it emerged gradually across US and Soviet Cold War strategic literature through the 1950s alongside second-strike and deterrence theory, with no one publication the sources agree is the origin. This atlas currently records 1950 only as an order-of-magnitude placeholder for the decade, per the entity's own origin-year StatusNote.
What would resolve this A specific, sourced founding publication or strategic-policy document that historians of nuclear strategy credit as first naming or formalizing first-strike doctrine as distinct from general preemptive-attack theory.
Openhistory of nuclear strategyWikipedia: First Strike (Nuclear Strategy)