UPDATE (1 Oct 2022): SPECIAL ISSUANCE PASSPORT (SIP) REQUIREMENT FOR GERMANY, JAPAN & THE REPUBLIC OF KOREA
Eligible family members and DoD civilians on official travel to Germany, Japan and the Republic of Korea must have either a 1. Special Issuance Passport (SIP) (i.e., Official Passport) or, 2. After applying for a SIP and if it cannot be obtained prior to departure, use of a Regular (Blue Tourist) Passport in lieu of the SIP is permissible for travel via MILAIR, contract or commercial air travel. See Electronic Foreign Clearance Guide (eFCG) for country specific requirements concerning official travel and the use of a SIP or contact your unit-level passport office.
eFCG Link: https://www.fcg.pentagon.mil/