After being delayed due to high winds and thick cloud/rain, the Cygnus OA-4 (Deke Slayton II) cargo vessel was finally successfully sent into orbit by an Atlas V 401 rocket launched from Cape Canaveral on 6 December at 2144 GMT. The mission, which was part of a commercial contract for NASA, was to deliver 3315kg of cargo to the International Space Station (ISS). It carried out the first of two Atlas V launches procured from United Launch Alliance by Orbital ATK after it suspended all of its Antares flights to allow an engine change. This followed the fiery explosive failure of the original Antares Cygnus Orb-3 (Deke Slayton) cargo mission in October 2011. The Deke Slayton element of the names is a tribute to the former NASA astronaut and manned spaceflight executive.
On 9 December 2015, the craft was captured by the ISS robot arm at 1119 GMT. It was later berthed and locked in position at 1426 GMT on the Earth-facing port of the Unity module.