Why interwar states unified naval and military air power

Why did interwar countries merge their air arms into a single force despite the concept's later shortcomings?

They expected lower costs and believed air specialists should control an indivisible new form of warfare, but this often neglected naval aviation's distinct operational and maintenance needs.

Unified air forces promised savings and rested on the claim that air power was indivisible. Strategic-bombing theory strengthened the argument for putting aviation under an independent service. Douhet's expectations depended on aircraft carrying enormous bomb loads and chemical weapons, judged unrealistic for the period envisaged. In Britain, the Royal Flying Corps accused the Royal Naval Air Service of gaining an unfair advantage in procurement. The explanation offered is that naval orders included spare parts alongside the aircraft and equipment. The criticism of the unified service is that it took far too long to adopt that sustainment practice.