What is martin xb-68?

The Martin XB-68 was a proposed American high-altitude reconnaissance aircraft designed by the Glenn L. Martin Company in the 1950s. It was intended to replace the aging RB-57D and RB-47E strategic reconnaissance aircraft in the United States Air Force. The XB-68 was a large aircraft with a wingspan of over 150 feet, and was designed to fly at high altitudes, with a proposed operational ceiling of 70,000 feet. It was powered by four Pratt & Whitney J75 turbojet engines, and had a range of over 5,000 miles. However, the XB-68 project was canceled in 1957 due to changes in military strategy and budget cuts, and no examples were built.