The United States Navy sought an all-weather carrier-based attack aircraft to replace the Douglas A-1 Skyraider after its service in the Korean War, and the Grumman A-6 Intruder emerged from a 1955 request for proposals that drew 11 designs from Boeing, Lockheed, Bell, Grumman, Douglas, Martin, Vought, and North American for a two-seat, subsonic attack bomber with side-by-side seating to reduce cockpit workload. Grumman's A25-1 design received the contract and entered production in 1958, leading to the A-6, which was introduced in 1963 and served as the Navy's and Marine Corps' premier medium and all-weather attack aircraft through the 1990s. Its twin Pratt & Whitney turbojets required forward intakes that gave the aircraft a swollen, ungainly appearance, while its rounded, streamlined rear inspired jokes that it was backwards. The pilot sat on the left and the bombardier-navigator on the right, a layout valued because it gave the navigator greater access to cockpit tasks such as monitoring airspeed, power settings, rate of descent, and altitude. The Intruder's avionics included Forward Looking Infrared, laser targeting, Low Light Level TV, and Moving Target Identification, but its major advance was Digital Integrated Attack and Navigation Equipment, or DIANE, which calculated the proper moment to release a payload by factoring in speed, rate of climb, angle of dive, G force, wind, and altitude. DIANE's Vertical Display Indicator also gave the pilot a representation of the horizon, sky, terrain, radar altitude, and angle of attack, helping the A-6 fly close to the terrain and excel at low-level bombing.