The Delta II is the work horse of the American launch vehicle inventory.  It currently flies between 14 and 16 times each year, more than any other US launch vehicle, delivering a range of government, scientific and commercial payloads.  In addition to a number of high profile NASA missions, the Delta II has recently deployed a large bulk of the Iridium and Globalstar LEO constellation satellites.

The current Delta launch vehicle can trace it's origins to the early days of American rocketry and the Thor-Delta launch vehicles.   Today, there are several variants of the Delta II.  The Delta 7900 series uses nine GEM's and can place approximately 11,000 lb into an easterly LEO orbit.   By adding a Star 48 third stage motor, the Delta 7900 can place 4,475 lb into a 28 degree GTO orbit.   The Delta 7300 series uses the Delta core with three Graphite Epoxy Motors (GEM's).  The Delta 7400 series uses the Delta core with four GEM's.  The 7300 and 7400 series are used primarily to launch NASA "Med-Lite" missions as well as commercial missions which do not require the full payload capability of the 7900 series vehicle.