Jimmy is still in the US, although the return address he uses will be his oversees mailing address. When he does go overseas he will have more training before going into combat. This letter does not include a written date but it is most likely from either July 17 or 24.
Jimmy just arrived at Barksdale Field, LA and has not yet been moved to a squadron. He praises the architecture and atmosphere of the Barksdale camp. On the way there, they got to stop in New Orleans.