In late June 1941, the design bureau of plant No 289 developed a design for a single-seat twin-engine armoured attack aircraft (SSTEAAA) with two M-71 engines. By the autumn, the design was completed, with two gun posts added and the crew fleshed out with an air gunner.
The design of a two-seat twin-engine armoured attack aircraft (TSTEAAA) was approved by the leadership of PCAI and AFRA, and the design bureau of O.P. Sukhoi started to build a mock-up of the aeroplane. In October 1941, the mock-up was approved, but the evacuation that began made it impossible to proceed with the design and building of TSTEAAA until May 1942.
Once resumed, the aeroplane's design moved forward at a fast pace and as early as 20th September a complete set of drawings was made available to the manufacturer. In August 1942, efforts were launched to build an airframe for static trials and two flying prototypes of the aeroplane. TSTEAAA was being built using the facilities of engine plant No 19 in the town of Molotov (now Perm), where pilot-production plant No 289 was set up when evacuated. The first prototype was scheduled for completion in early May; a second one, in August 1943.
In late January 1943, the Air Forces Commander-in-Chief approved the conceptual design of the TSTEAAA version, with a high-altitude recon plane and medium bomber as variants, requesting that this design be incorporated in the second TSTEAAA prototype.
At the beginning of August 1943, the P.O. Sukhoi design bureau was moved back to its original location and the first TSTEAAA prototype (Su-8) was brought to the town of Tushino near Moscow, where plant No 289 had been relocated. Work to improve the aircraft was resumed, the plane having been fitted out with a higher-capacity engine, the M-71F.
By the beginning of December 1943, the Su-8 performed a series of taxiing manoeuvres on the ground and in the air on the plant's airfield, which revealed a number of faults whose elimination lasted till the end of winter.
On 11th March 1944, the plant's test pilot N.D. Fikson took the Su-8 off the ground for its maiden flight. The manufacturer's flight tests went on, with brief intermissions, till the end of 1944. By that time, there was no longer any apparent urgency to produce a new attack aircraft for the Air Forces. Moreover, work on the M-71F engine was scaled down. All this finally put a stop to the work on the Su-8 aeroplane itself.