The Grumman E-2 Hawkeye is an American all-weather, aircraft carrier-capable tactical airborne early warning (AEW) aircraft. This twin-turboprop aircraft was designed and developed during the late 1950s and early 1960s by the Grumman Aircraft Company for the United States Navy as a replacement for the earlier E-1 Tracer, which was rapidly becoming obsolete. E-2 performance has been upgraded with the E-2B, and E-2C versions, where most of the changes were made to the radar and radio communications due to advances in electronic integrated circuits and other electronics. The fourth version of the Hawkeye is the E-2D, which first flew in 2007. The E-2 also received the nickname "Super Fudd" because it replaced the E-1 Tracer "Willy Fudd". In recent decades, the E-2 has been commonly referred to as the "Hummer" because of the distinctive sounds of its turboprop engines, quite unlike that of turbojet and turbofan jet engines. The E-2 and its sister, the C-2 Greyhound, are currently the only propeller airplanes that operate from aircraft carriers. In addition to U.S. Navy service, smaller numbers of E-2s have been sold to the armed forces of Egypt, France, Israel, Japan, Mexico, Singapore and Taiwan.