Complex sentence: The 150 NA-91s were designated P-51 by the newly formed USAAF and were initially named Apache, although this was soon dropped and the RAF name, Mustang, adopted instead.
Split into simpler sentences: The 150 NA-91s were designated P-51 by the newly formed USAAF and were initially named Apache. This name was dropped soon and the RAF name, Mustang, adopted instead.