O7 means Officer grade: Commodore, Rear Admiral Lower Half, or Brigadier General in Military
Similar to O7
121ARW - 121st Air Refueling Wing129 RQW - 129th Rescue Wing
12N - Horizontal Construction Engineer
13 SCVI - 13th South Carolina Volunteer Infantry Regiment
13AD - 13th Airborne Division
13B - Military Occupational Specialty code for Cannon Artilleryman
147FA - 147th Field Artillery Regiment
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