Which of the following is NOT one of the core values of the Marine Corps?

The core values of the Marine Corps are defined by honor, courage, and commitment. Among the choices, honor is one of these core values, emphasizing the importance of integrity and ethical conduct. Integrity itself is closely related to the core values, representing the quality of being honest and having strong moral principles.

Honesty, while a vital characteristic and closely associated with integrity, is not officially listed as one of the Marine Corps' core values. Fortitude, on the other hand, represents mental and emotional strength in facing adversity but is not one of the foundational values that the Marine Corps identifies. The distinction here is important in understanding the specific terminology and values that guide Marines in their conduct and service.

Thus, "Fortitude" is the correct answer as it is not classified as one of the three core values of the Marine Corps, which are honor, courage, and commitment.