To replace around 110 aging Lockheed Orion P-3 Maritime Patrol Aircraft (MPA), in March 2000 the US Navy drew up a requirement for around 150 new multi-functional aircraft and named the programme the Multi-mission Maritime Aircraft (MMA). The competition soon narrowed down to two aircraft, a version of the Boeing 737-800 and a new version of the Lockheed P-3 Orion, named the Orion 21.

The Lockheed Orion21 was intended to be a “rugged, all new-production weapon system based on the proven P-3 airframe that reflecting six decades of Maritime Patrol and Reconnaissance experience”. Salient features were:

• New Pratt & Whitney PW150 engines, originally used for regional turboprops, with Hamilton Standard eight blade all composite propellers, with individual blade replacement.
• Open systems architecture avionics featuring a fully-digitized all glass cockpit.
• Logistics support programme focused on real time fleet health assessment.
• 50 per cent increase in mission range and endurance over legacy systems. Lockheed Martin selected a turboprop engine because it believed this would provide optimal performance in the ASW mission. The company claimed this would give the aircraft 25% more power, 60% more thrust and burn 27% less fuel then a turbofan - a direct challenge to Boeing's proposed MMA trubofan powered 737.

However, Lockheed’s efforts were in vain and on 14 Jun 2004 the US Navy awarded the MMA contract to Boeing and their 737-800 known as the P-8A. A great many countries intend to continue operating their P-3 Orions for many years to come, although many of these 14 operators have expressed an interest in acquiring an updated version of the P-3, it seems unlikely that the Orion 21 would ever be commercially viable without the MMA contract.