The Pony Express was a UNSC corvette. As of 2552, it was the fastest ship avaliable to the UNSC.
During The Second Battle of Earth, The Pony Express was at Earth fighing the Covenant. After recieving a message from Dr. Halsey, Lord Hood planned on sending the Spartan-IIs to Onyx aboard the Pony Express, but they opted to instead capture a Covenant destroyer, the Bloodied Spirit, which was faster than even the Pony Express.