Wikipedia:Today's featured article/July 31, 2015

Airborne Interception radar, Mark IV, was the first successful air-to-air radar system, used in Britain's Bristol Beaufighter heavy fighters by early 1941 in the Second World War. Early development of the Mk. IV was prompted by a 1936 memo from the inventor Henry Tizard to Robert Watt, director of the radar research efforts, who agreed to allow physicist Taffy Bowen to form a team to study the problem of air interception. The team had a test bed system in flights later that year, but progress was delayed for four years by emergency relocations, three abandoned production designs, and Bowen's increasingly adversarial relationship with Watt's replacement, Albert Percival Rowe. The Mk. IV had many limitations, including displays that were difficult to interpret, a maximum range that decreased with the aircraft's altitude, and a minimum range that was barely close enough to allow the pilot to see the target. Nevertheless, the Mk. IV played a role in the Royal Air Force's increasingly effective response to The Blitz, the Luftwaffe night bombing campaign. The Mk. VIII largely relegated the Mk. IV to second-line duties by 1943.