Most Wiccans meet with a coven, a small group of people. Each coven is autonomous. Most are headed by a High Priestess, often with the assistance of a High Priest. Some are headed by a High Priestess or High Priest without a partner, and some regard themselves as a gathering of equals. Covens can be of mixed gender, or all female or male, depending on the preferences of the members.
Every initiate is considered to be a priestess or priest.
Most covens are small. Thirteen is the traditional maximum number of members, although not an absolute limit. At that size covens form a close bond, so Wiccans in the military are likely to maintain a strong affiliation with their covens back home. A typical difference would be that more traditional groups would tend to follow a set liturgy, whereas eclectic groups would emphasize immediate inspiration in worship. These distinctions are not particularly important to the military chaplain, since it is unlikely that enough members of any one Tradition would be at the same base.