The Boeing P-8 Poseidon is the successor to the venerable P-3 Orion, which had been in service for half a century before the first P-8 entered squadron service. Compared to the turboprop P-3, the P-8 is based on the 737-800 airliner airframe although it borrows certain fuselage and wing components from other Boeing designs. Initial P-8s were installed with legacy systems from P-3s set for replacement but these will be eventually fitted with newer equipment. One major difference is the lack of a magnetic anomaly detector (MAD) as a result of the P-8s higher operating altitude. The aircraft can be equipped with a variety of weapons including Harpoon missiles, mines, bombs, and also features High Altitude Anti-Submarine Warfare Weapon Capability (HAAWC) which allows a Mark 54 torpedo to be launched as a glide bomb. Eventually, P-8s will also be equipped with MAD-equipped drones for lower-altitude sub-hunting. The P-8 is currently in service with USN in small numbers and budget difficulties (as well as technical issues in the first production aircraft) make it likely that the process of replacing P-3s will take longer. The only other foreign user is India and New Zealand is expected to also make an order. Numerous other countries are expected to show interest over the coming years.

First flight of the converted 737-800 took place on 25 April 2009 and entered service in 2012 as the P-8A. Indian Navy versions are known as the P-8I and differ in having a downgraded APY-10 surface search radar. The P-8 AGS (Airborne Ground Surveillance) was a proposed version to replace the USAF's E-8 but has not been accepted.