What was one key achievement of the first Chief of Staff of the Air Force?

The correct answer highlights a significant milestone in the evolution of the U.S. Air Force under its first Chief of Staff, General Carl A. Spaatz. One of his paramount achievements was the development and establishment of strategic air power as a vital component of military operations. This focus on strategic air power emphasized the importance of air superiority and the ability to project power from the air in support of national defense strategies. Spaatz's leadership during the early years of the Air Force, including his advocacy for the use of long-range bombers and the integration of air power into joint military operations, laid the groundwork for how air power would be utilized in future conflicts.

The other choices, while relevant in the broader context of military development and structure, do not directly pertain to the achievements of General Spaatz. The creation of the National Guard and the introduction of combat aircraft were not specifically his contributions as the first Chief of Staff, nor did he directly reorganize the military service structure in a transformational way. Instead, his focus on strategic air power significantly shaped the future of the Air Force and its operational strategies.