Delta IV left active service in 2023 with its final launch, 19 years after its debut. In its last few years of service only the Delta IV Heavy variant saw use. Delta IV had a unique launch profile that typically involved slight charring of the insulation on the boosters during launch due to excess hydrogen in the air - this did not cause damage to the vehicle.
Originally developed and operated by Boeing, Delta V Heavy would come to ULA as part of Boeing's contribution to the formation of ULA>.
