Which of the following is a basic department of defense communication network?

NIPRNET, or the Non-classified Internet Protocol Router Network, is the correct answer because it is the Department of Defense's primary communication network that facilitates the transmission of unclassified information. It allows users to send emails, browse the internet, and communicate securely within the framework of the military and other government agencies.

NIPRNET is designed to provide a reliable and consistent platform for non-classified communications, ensuring that personnel can access necessary information and communicate efficiently. The network supports various applications that are crucial for everyday operations and inter-departmental collaboration, making it essential for the functioning of the Department of Defense.

In contrast, the other options do not represent basic communication networks that are specifically designated for the Department of Defense's general use. FWI, CMNET, and XNET either denote networks that are not widely recognized or do not have the specific purpose and designation that NIPRNET has within the Defense infrastructure.