However, in the mid-80s, advocacy groups, such as MADD (Mothers Against Drunken Drivers) lobbied Congress to change this. Federal law (United States Code, Title 10, Section 2683) requires military installation commanders to adopt the same drinking age as the state the military base is located in. The only exception to this rule is if the base is located within 50 miles of Canada or Mexico, or a state with a lower drinking age, the installation commander may adopt the lower drinking age for military personnel on base.
This law is also codified in DoD Instruction 1015.10, which states:
The minimum drinking age on a DoD installation located in a State (including the District of Columbia) shall be consistent with the age established by the law of that State as the State minimum drinking age. Minimum drinking age means the minimum age established for persons who may purchase, possess, or consume alcoholic beverages.
In the case of a DoD installation located in more than one State or in one State but within 50 miles of another State or Mexico or Canada, the minimum drinking age on that DoD installation shall be the lowest applicable age of the State in which the DoD installation is located or the State or jurisdiction of Mexico or Canada that is within 50 miles of such DoD installation.
The minimum drinking age on a DoD installation located outside the United States shall be 18 years of age. Higher minimum drinking age will be based on international treaties and agreements and on the local situation as determined by the local installation commander.
The commander of a DoD installation may waive the above requirements, if such commander determines that the exemption is justified by special circumstances. Special circumstances are those infrequent, non-routine military occasions when an entire unit, as a group, marks at a military installation a uniquely military occasion such as the conclusion of arduous military duty or the anniversary of the establishment of a military service or organization. The event must be held on a military installation. The commander shall ensure that appropriate controls are in place to prevent endangering Military Service members or the surrounding community.
While the law and DOD Directive allow drinking on-base by those under the age of 21 if the base is located within 50 miles of a country that allows a lower drinking age, the Secretary of the Navy issued a Navy policy (which included the Marine Corps), which prohibited the practice. Until then, on-base drinking by sailors and Marines on bases within 50 miles of Mexico (such as Camp Pendleton) was common.
A couple of years later, the Army followed suit, prohibiting on-base drinking on its bases (such as Fort Bliss, Texas and White Sands Missile Range) which were within 50 miles of Mexico. The Air Force never did allow installation commanders to adopt the "50 mile rule."
In 1997, the Marine Commandant issued a policy which restricted on and off base drinking for Marines stationed overseas to age 21, even if the host-country had a lower drinking age law.
But in September 2006, the Corps lowered the drinking age for Marines in Japan to 20 to reflect the local drinking age.
With respect to the "special circumstances" rule, I should point out that all of the services require the installation commander to get special permission from their respective service headquarters in order to lower the drinking age for these special events. For example, if an Air Force Installation Commander wanted to lower the drinking age requirement for a party to celebrate the Air Force's "Birthday," he or she would need permission of the office of the Air Force Chief of Staff. Because a commander would be literally "sticking their neck out," (in case something happens), in my experience, such permission is almost never requested.
However, The Marines may have a different philosophy. In April 2007, the Marine Corps Commandant signed off on MARADMIN 266/07, allowing 18-year-old Marines to drink in foreign ports if the host nation’s law allows it.
The message also gives the "green light" for Marine Corps commanders to have parties on base where 18 year old Marines can drink, during infrequent special occasions, such as a unit's return from combat deployment, or during the Marine Corps' Birthday Ball. The directive mandates that commanders "ensure that appropriate controls are in place to prevent endangering Military service members or the surrounding community," during such events.