What is the abbreviation for the Department of Defense?

The abbreviation for the Department of Defense is "DoD." This acronym is widely recognized and used to refer specifically to the United States Department of Defense, which is responsible for coordinating and supervising all agencies and functions of the government related directly to national security and the military. The structure and formation of the abbreviation "DoD" follows a common linguistic pattern in English where the first letter of each significant word is taken, making it both succinct and easily recognizable.

The other options do not conform to this standard or represent the Department of Defense accurately. "DofD" does not reflect the correct initials and adds unnecessary letters. "DoD-Defense" unnecessarily prolongs the abbreviation by including the word "Defense,” which is redundant in this context because "DoD" already signifies that the department is related to defense. "DeptD" mistakenly abbreviates "Department" as "Dept," which is not a commonly accepted abbreviation for this specific department, and it also alters the recognizable structure of the official name.