That would be an Evergreen Boeing 747–100, which reportedly reached Mach 1.25 in an uncontrolled dive.
The Evergreen Boeing 747–100, N475EV. The 747–100 was certified at a maximum takeoff weight between 333 to 340 tonnes.
Commenting later on the event in the Chicago Times, a Boeing spokesman said:
“Original flight tests of 747s conducted in 1969 and 1970 took 747-100 models to speeds of Mach 0.99. In addition, Boeing knows one case in which a 747 operated by Evergreen International made an emergency descent at speeds that exceeded Mach 1.”
The largest aircraft that was designed to fly at Mach 2.0 is the Tupolev Tu-160(Russian: Туполев Ту-160 Белый лебедь, romanized: Belyj Lebeď, lit. ’White Swan’; NATO reporting name: Blackjack).
At 275 tonnes, it is the heaviest aircraft ever to go supersonic regularly.
The mighty North American Aviation XB-70 Valkyrie is by far the largest aircraft designed to fly at Mach 3.0.
The Valkyrie had a MTOW of 245 tonnes.
The XB-70 explored supersonic flight riding on compression lift due to the supersonic waves it was creating. This is the ultimate waverider.
Concorde remains the largest aircraft to supercruise at Mach 2.0. The aircraft had an MTOW of 185 tonnes. The aircraft was powered by the mythical Rolls Royce/SNECMA Olympus 593 afterburning turbojet.
Concorde is the largest aircraft of any type to supercruise in supersonic flight at any Mach number. Not only that, Concorde’s supercruise capability is well ahead of that for any other aircraft. Concorde is the only aircraft with supercruise capability not powered by turbofan engines.
All others of comparable weight or larger must make use of afterburners/relight in order to sustain supersonic flight.
The Lockheed Martin F-22 Raptor and Eurofighter Typhoon, powered by turbofan engines are the fastest amongst supersonic aircraft military, in achieving Mach 1.5 supercruise.
The duration of that supercruise capability — in excess of 3 hours unaided, is also by far the greatest of any supersonic aircraft.
Further, the total time spent in supersonic flight for Concorde is greater than that for all other supersonic aircraft combined.