When the US Navy introduced the Boeing P-8A Poseidon, it did a lot more than trade turboprop engines for turbofans. The military-grade 737 Next Generation is the successor to the Lockheed P-3C Orion Maritime Patrol and anti-submarine warfare aircraft. The Orion was a 1960s-vintage submarine hunter made to serve in the Cold War to track and deter Soviet submarines. Made for the 21st-century battlefield, the Poseidon is a much more flexible and capable intelligence, surveillance, and reconnaissance aircraft that can outperform the Orion and Maritime Patrol and reinvent ASW tactics. The plane can carry torpedoes and sea mines, and crews...