The Master Chief arrives on Earth in east Africa, where he is found by Johnson and the Arbiter. The Chief and company return to a UNSC outpost where Keyes and Lord Hood plan a final effort to stop the Covenant leader, the High Prophet of Truth, from activating a Forerunner artifact the Covenant have excavated. The Chief clears anti-air Covenant defenses so Hood can lead the last of Earth's ships against the Prophet, but Truth activates the buried artifact, creating a slipspace portal which he and his followers enter. A Flood-infested ship crash-lands nearby; Elite forces arrive and vitrify the Flood-infected areas of Earth, stopping the threat. Following a message Cortana left aboard the Flood ship, the Chief, Arbiter, Elites, Johnson, Keyes and their troops follow Truth through the portal. Joining them is 343 Guilty Spark, who aids the Chief as he has no function to fulfill after the destruction of his ringworld.
Gameplay focuses on the "Golden Triangle of Halo": players utilize weapons, grenades, and melee attacks, which are available to a player in most situations. Players may dual-wield some weapons for additional firepower, forgoing the use of grenades and melee attacks. Unlike previous installments, the player's secondary weapon is visible on their player model, holstered or slung across the player's back. Halo 3 introduces support weapons, cumbersome two-handed weapons that slow the player when carried, but offer greatly increased firepower in return.
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