The Grennian Defence Force was established upon the Republic of Grennia's independence on 6 May, 2005. It is a volunteer-only defence force, so a draft does not exist.

As of 2025, it currently has approximately 30,000 active duty service members, with over 50,000 reserve troops.

The military is divided into three branches; the Army, Navy, and Air Force.

Within the Republic of Grennia, there a handful of military bases for each branch.

The Grennian Army currently has one base, located in Bokamang, Gekogashira City.

The Grennian Navy has two bases, one on Peninsula Point in Satogeko City and one in the Seaport Zone in Keromatsu City.

The Grennian Air Force operates out of a section of Gekkouga City Airport.

Domestically, the Grennian Defence force has the sole purpose of defending the Republic of Grennia from threats to its national security or armed invasion. Internationally, the Defence Force is primarily used for overseas peacekeeping missions and mediation.

Grennia also adopts a stance of neutrality on global affairs, and thus does not host any permanent foreign military presence.