Siege of the Atlas Moons
From Halopedia, the Halo wiki
In the Siege of the Atlas Moons UNSC forces fought the Covenant on the moons of the planet Atlas. UNSC forces won on ground, but where defeated in the massive space battle that ensued.
Little is known of this battle except that Vice Admiral Danforth Whitcomb fought in the engagement and gained a reputation as a great military commander.