The US Air Force studied various improvements to the AGM-158, resulting in the development of the JASSM-Extended Range (JASSM-ER), which received the designation AGM-158B in 2002. Using a more efficient engine and larger fuel volume in an airframe with the same external dimensions as the JASSM, the JASSM-ER is intended to have a range of over as compared to the JASSM's range of about . Other possible improvements were studied but ultimately not pursued, including a submunition dispenser warhead, new types of homing head, and a new engine giving ranges in excess of . The JASSM-ER has 70% hardware commonality and 95% software commonality with the original AGM-158 JASSM.