While mauler is correct in stating that there are currently no corvettes in operation with the US Navy, there are plans underway to introduce the LCS (Littoral Combat Ship) to the US inventory. This vessel, slated to be on the order of 2000 tons displacement, qualifies as a corvette under most definitions. It is considerably larger than most patrol ships, while being smaller than virtually any ship classified as a frigate, such as the Russian Neustrashimy or the US Perry-class.
The LCS' armament is also in keeping with traditional corvette designs, consisting of a single Bofors 57mm automatic cannon, six tubes firing either Mark 46 or Mark 50 anti-submarine torpedoes, a vertical launcher for Evolved Sea Sparrow Missiles and a 22-cell launcher turret for rolling airframe missiles. Additional secondary armament could consist of several 12.7mm or 7.62mm machine guns. It is also equipped with a flight deck and hangar allowing it to operate a single MH-60R Seahawk anti-sub/anti-surface helicopter. The Seahawk contributes significantly to its overall firepower by substantially extending its effective range against submarines and also allowing the deployment of the AGM-119 Penguin anti-ship missile
Designed with a single planing hull form (like most modern light warships), the LCS is capable of high speeds. The design specifications call for a maximum speed of 50 knots, though the maximum speeds achieved by the prototypes are still not published. Power is provided by gas turbine engines of unspecified type (though likely smaller than the LM2500s used on the Arleigh Burke-class).
The LCS is designed to be modular, allowing major parts of it, including the sensors and weapons fit, to be modified without a major overhaul. In theory, this allows a squadron of LCSes to be optimized for various missions: one for anti-aircraft warfare, by swapping out the 57mm gun for another missile launcher, still another for anti-ship warfare by replacing the ESSMs with Standard missiles, and another for surface fire support by fitting another 57mm, for example. In practice, this may prove to be more troublesome or expensive than its benefits warrant.
The first two LCSes were ordered in 2005, and are due to be commissioned some time in 2007.