While unable to put up much of a fight head-to-head, the UNSC was able to put up a stiff defense against the Covenant using superior tactics and sheer numbers to slow their advance down considerably.
ALL UNSC WARSHIPS
It has been said that were it not for the insurrection, humanity would have likely been overrun by the Covenant far more quickly than it was. Because of growing unrest in the outer colonies, the UNSC was forced to accelerate the development of space-borne weaponry, the majority of focus being on ships of war. By the start of the war with the Covenant, the UNSC had a sizable, though still underpowered, fleet of warships. Still, the Covenant slowly ate into human space, leaving a wake of destruction of hundreds of UNSC warships.