Senior officers are usually only addressed by their rank.
Senior officers are usually only addressed by their rank.

The military has strict procedures on how to behave and respond in a seemingly endless number of situations. There is a protocol for everything including how to address other enlisted personnel. Personnel are usually addressed by their rank followed by their last name. Only in agreed upon personal communication are first names used.

Confusion

The primary reason the military uses last names when addressing each other is to avoid confusion. A company or squad may have several people with the same first name. For example, a common name like John or Michael may be the first name of several of the men. It is less likely that the troops will have the same last name, although it is possible. When delivering orders in battle, having to clarify which John the order is for can cost valuable seconds.

Formality

Last names are also more formal. The military is a conservative and formal institution. Addressing a person by the last name shows respect and is professional. It keeps the interaction between troops formal. It also shows equality as all troops are referred to by superior officers by their last names.

Distance

The use of last names also creates a distance and makes the relationship less personal. The use of first names implies a personal relationship, something that may not be advantageous for the troops to adopt. If senior officers referred to junior officers by their first names, the junior ones may feel more at liberty to question orders due to the perceived personal interaction.

Similar Names

In the case of similar or identical last names, the first initial of the first name is used before the last name. For example, if their are two enlisted personnel, one with the name John Coleman and the other Michael Coleman, both men can not be called Coleman. One would be called J. Coleman and the other M. Coleman.