Shipping to overseas US military bases is considered as export operation by stamps and requires customs information. You need to specify UNIT PRICE for each item you ship in this order in 3PL, then delete & reimport order in techship.
Below is link for Military Mail Guide at stamps.com:
http://www.stamps.com/whitepapers/usps-military-mail-guide.pdf
http://www.stamps.com/whitepapers/usps-military-mail-guide.pdf