The Raytheon Sentinel is an airborne battlefield and ground surveillance aircraft formerly operated by the Royal Air Force (RAF). While based on the Bombardier Global Express ultra long-range business jet, the prime contractor for the Sentinel was the American defence firm Raytheon, which supplied most of the mission systems and performed the integration work.

Originally known as the ASTOR (Airborne STand-Off Radar) programme, procurement of the type started during 1999. Following its delivery in 2007, the Sentinel fleet was operated by an RAF squadron manned by both air force and army personnel. The Sentinel is interoperable with other allied systems such as JSTARS and the NATO Alliance Ground Surveillance (AGS) system. Sentinels have been deployed overseas on multiple occasions, such as in support of the British Army in Afghanistan, coalition forces in Libya, and to assist French forces deployed in Mali. The type also saw smaller-scale deployments in Ghana and even domestically to assist disaster relief operations.

In 2010, the British government's Strategic Defence and Security Review (SDSR) announced its intention to "withdraw the Sentinel airborne ground surveillance aircraft once it is no longer required to support operations in Afghanistan." The 2010 decision was reversed in 2014 by Prime Minister David Cameron and in the 2015 SDSR, the British government announced that the type's retirement would be delayed and that it would remain in service "into the next decade". Due to the repeated equivocations over its future, the Sentinel did not receive upgrades during its service life. The type was retired in March 2021.