Which of the following is NOT a method of communication in defense?

In a military context, communication methods are crucial for coordinating actions and relaying information, especially in defense situations. The use of wire, messenger, and radio are all traditional and established forms of communication that have been utilized in various defense operations.

Wire communication involves using physical lines to transmit messages, which can be secure and reliable, particularly in combat situations where electronic signals might be compromised. Messenger systems leverage human couriers to deliver messages, providing a direct and personal means of communication, often used when electronic means are unavailable or deemed insecure. Radio communication is vital in modern defense operations, allowing for real-time voice communication over various distances, which is essential for maintaining situational awareness and command and control.

In contrast, email, while a recognized form of communication in many civilian and organized settings, is generally not suited for immediate and secure communications in the context of defense operations. Email relies on networks and electronic infrastructure which may not be reliable or secure in a military environment, especially under combat conditions where immediate, direct communication is often necessary. Therefore, email does not align with the traditional methods employed in defense, making it the correct answer to identify as NOT being a primary method of communication in that context.