P-8A Poseidon: The US Navy's Newest Maritime Patrol & Antisubmarine Aircraft. John Gourley. The P-8A Poseidon, a variant of the Boeing 737 series of airliner, takes over the role of antisubmarine warfare from the P-3 Orion, itself a derivative of an airliner, the Lockheed Electra. The P-8A brings new capabilities, endurance, and crew enhancements to the art form of maritime patrol, surveillance, and reconnaissance. 9" x 9".