The A-2 visa is a non-immigrant visa which allows travel to United States for certain government officials, employees, their immediate families, and their technical and support staff. This includes military personnel traveling for reasons not related to NATO. Those typically admitted under an A-2 visa include:
There is no maximum limit on the duration of stay for A-2 visa holders, and no requirment to maintain a foreign residence.
References
A-2 visa Wikipedia(Text) CC BY-SA