The aircraft was officially sanctioned on 24 August 1965 under the internal codename T-6.
The first prototype, T-6-1, was completed in May 1967 and flew on 2 July with Vladimir Ilyushin at the controls.
The initial flights were performed without the four lift jets, which were installed in October 1967.
At the same time, R-27s were replaced with Lyulka AL-21Fs.
STOL tests confirmed the data from S-58VD that short-field performance was achieved at the cost of significant loss of flight distance as the lift engines occupied space normally reserved for fuel, loss of under-fuselage hardpoints, and instability during transition from STOL to conventional flight.
So the six-engine approach was abandoned.

By 1967, the F-111 had entered service and demonstrated the practical advantages and solutions to the technical problems of a swing-wing design.
On 7 August 1968, the OKB was officially tasked with investigating a variable geometry wing for the T-6.
The resulting T-6-2I first flew on 17 January 1970 with Ilyushin at the controls.
The subsequent government trials lasted until 1974, dictated by the complexity of the on-board systems.
The day or night and all-weather capability was achieved – for the first time in Soviet tactical attack aircraft – thanks to the Puma nav/attack system consisting of two Orion-A superimposed radar scanners for nav/attack, a dedicated Relyef terrain clearance radar to provide automatic control of flights at low and extremely low altitudes, and an  Orbita-10-58 onboard computer.
The crew was equipped with Zvezda K-36D ejection seats, allowing them to bail out at any altitude and flight speed, including during takeoff and landing.
The resulting design with a range of 3,000 kilometers (1,900 mi) and payload of 8,000 kilograms (18,000 lb) was slightly smaller and shorter ranged than the F-111.

Ten fatal accidents occurred during Su-24 development, killing thirteen Sukhoi and Soviet Air Force test pilots.

The first production aircraft flew on 31 December 1971 with V.T. Vylomov at the controls, and on 4 February 1975, T-6 was formally accepted into service as the Su-24.
 About 1,400 Su-24s were produced.
The aircraft was officially sanctioned on 24 August 1965 under the internal codename T-6. The first prototype, T-6-1, was completed in May 1967 and flew on 2 July with Vladimir Ilyushin at the controls. The initial flights were performed without the four lift jets, which were installed in October 1967. At the same time, R-27s were replaced with Lyulka AL-21Fs. STOL tests confirmed the data from S-58VD that short-field performance was achieved at the cost of significant loss of flight distance as the lift engines occupied space normally reserved for fuel, loss of under-fuselage hardpoints, and instability during transition from STOL to conventional flight. So the six-engine approach was abandoned.
By 1967, the F-111 had entered service and demonstrated the practical advantages and solutions to the technical problems of a swing-wing design. On 7 August 1968, the OKB was officially tasked with investigating a variable geometry wing for the T-6. The resulting T-6-2I first flew on 17 January 1970 with Ilyushin at the controls. The subsequent government trials lasted until 1974, dictated by the complexity of the on-board systems. The day or night and all-weather capability was achieved – for the first time in Soviet tactical attack aircraft – thanks to the Puma nav/attack system consisting of two Orion-A superimposed radar scanners for nav/attack, a dedicated Relyef terrain clearance radar to provide automatic control of flights at low and extremely low altitudes, and an  Orbita-10-58 onboard computer. The crew was equipped with Zvezda K-36D ejection seats, allowing them to bail out at any altitude and flight speed, including during takeoff and landing. The resulting design with a range of 3,000 kilometers (1,900 mi) and payload of 8,000 kilograms (18,000 lb) was slightly smaller and shorter ranged than the F-111.
Ten fatal accidents occurred during Su-24 development, killing thirteen Sukhoi and Soviet Air Force test pilots.
The first production aircraft flew on 31 December 1971 with V.T. Vylomov at the controls, and on 4 February 1975, T-6 was formally accepted into service as the Su-24.  About 1,400 Su-24s were produced.
Sukhoi Su-24