Spartan 3s are a small group of specialised Spartans codenamed "headhunters" and trained to do two person infiltrations. Any sort of thing that needs a hit man you can usually find a Headhunter has already done. They are the assassins of the UNSC, the best at what they do.
The Headhunters usually loose radio contact with everyone when inside a camp. If the soldier doesn't come back the UNSC refers to them as KIA.
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