Final answer:
The size of the DoD seal when used as a DON letterhead is usually around 1.25 inches in diameter.
Step-by-step explanation:
The size of the DoD (Department of Defense) seal when used as a DON (Department of the Navy) letterhead can vary depending on the specific design and layout of the letterhead. However, as per the official guidelines, the seal is usually around 1.25 inches in diameter. This size ensures that the seal is clearly visible and legible when printed on letterhead and other official documents.