What legislative action was pivotal in the formation of the Army Air Service?

The formation of the Army Air Service was significantly influenced by the National Defense Act of 1916. This act marked a major turning point in U.S. military organization, leading to the establishment of the Army Air Service as an integral part of the Army during World War I. It recognized the need for a dedicated aerial organization to support ground forces and facilitate military operations through air power. The act laid the groundwork for the subsequent development of air capabilities and the formalization of a separate air service within the Army.

The other responses provided do not pertain to the direct establishment of the Army Air Service. For instance, Executive Order 9981 addressed military desegregation and is unrelated to the genesis of the air service, while specific resolutions and bills like the ones mentioned do not relate to the structural changes initiated by the National Defense Act.