From Halopedia, the Halo wiki
The Bulldogs were a joint Navy-Marine Corps unit attached to UNSC Infinity during the investigation of the Forerunner shield world Requiem. They were led by Chief Petty Officer Peters. When Infinity crash-landed inside the shield world in July 2557, the Bulldogs were sent into the surrounding swamps for reconnaissance and later to assist nearby Marines. They were eventually killed by Promethean constructs.
Chief Petty Officer Peters' leadership of the Bulldogs suggests that they were a Naval Special Warfare unit.
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