In 1938, BB-1 was used as the platform to start design of a ground-attack aircraft (GAA). Compared to its prototype, it featured an M-88 engine, strengthened armour, modified landing gear design and a number of other differences. The GAA aeroplane (BB-2) passed into testing in the summer of 1940.
The customer having upgraded the attack aircraft requirements, in the summer of 1939, the design bureau of P.O. Sukhoi started to develop a conceptual design of a single-seat armoured attack aircraft. In the autumn, the SSAAA design was accepted and approved.
A 4th March 1940 resolution of USSR CPC Defence Committee P.O. Sukhoi was officially given the job "To design and build a single-engine armoured single-seat attack aircraft with the M-71 engine… The aircraft to be built in a set of two prototypes…"
Work on the first prototype began in mid-April 1940 and dragged on till late January 1941, which was due to the Design Bureau moving to a new location, the inadequate production infrastructure of plant No 289 and the unavailability of the M-71 engine.
On 1st March 1941 pilot A.I. Kokin started an accelerated programme of manufacturer's tests, which continued till late August. The tests established that in terms of flight speed, rate-of-climb and takeoff and landing performance, the M-71 Su-6 was vastly superior to the AM-38 Il-2, but lack of cannon and missile armaments posed a serious obstacle to its production. Between 25th September and 10th October, the aeroplane underwent verification tests at the AFRA Scientific Research Institute. The tests were never completed in full as the only available M-71 engine reached its age limit.
The second Su-6 attack aircraft prototype under construction was completed in January 1942. In contrast to the first prototype, it featured two VYa-23 ShKAS cannons, four ShKAS machine-guns and ten RE for PS-82 or PS-132.
The manufacturer's tests of the aeroplane were conducted between 15th January and 23rd February, and it was then handed over to the AFRA Scientific Research Institute for governmental tests on the 24th February. These continued, on and off, till late May 1942. The governmental testing report said:
"…The Su-6 aeroplane with M-71 engine in terms of top level-flight speed surpassed the AM-38 Il-2 attack aircraft…
…After execution of a combat mission… the Su-6 aeroplane has a top speed… of 483kph on 10-minute boost. This speed puts the Su-6 aeroplane out of reach of enemy fighters with their minor advantage in speed…
… It is recommended to build a small field-use batch of Su-6 aircraft with the M-71, the aircraft being promising in terms of its relatively high level speed and high-performance gun-and-cannon and missile armaments…"
A draft SDC resolution was produced in June to authorise field-use batch production of 25 Su-6-w/M-71 single-seat armoured attack aircraft by 15th December 1942, but unfortunately, the issue was never settled. P.O. Sukhoi, having taken into account all the comments and faults that had come to light during the governmental tests and secured authorisation from A.I. Shakhurin, started to build a modified Su-6. By the end of December, a modified Su-6 with the M-71F was for all intents and purposes completed, but in the light of altered requirements for the attack aircraft, P.O. Sukhoi made the decision to convert it into a two-seater. On 6th March 1942, pilot N.D. Fikson took the two-seat Su-6 off the ground; by mid June, the manufacturer's tests were completed and the aeroplane handed over to the AFRA Scientific Research Institute for governmental testing.
The Su-6 M-71F passed the governmental tests with flying colours. It was ascertained that in terms of maximum speeds, rate-of-climb, ceiling and range it was vastly superior to the AM-38F Il-2 combat aircraft in the AFRA inventory. But it proved impossible to set up mass production of the M-71F engine under the difficult wartime conditions. That is why P.O. Sukhoi was ordered to substitute a lower-capacity AM-42 engine for the M-71F.
On 22nd February 1944, G.I. Komarov started the manufacturer's trials of the Su-6 attack aircraft with the AM-42. Upon completion of the manufacturer's tests, at the end of April, the aeroplane was made available for governmental tests, which were suspended on 15th May as a result of the failure of the AM-42 to meet its projected performance.
May 1944 saw successful completion of governmental testing of the AM-42 Il-10 attack aircraft, which demonstrated high flight capabilities. Comparison between the Su-6 variant with the AM-42 and the Il-10 in terms of FP did not favour the former. The Sukhoi attack aircraft proved inferior to the Ilyushin machine in terms of most key indicators. In the final analysis, it was found that it did not make sense to put the Su-6 with the AM-42 into mass production.
In 1943, P.O. Sukhoi was awarded a Stalin Prize of the 1st Level for the development of the Su-6 armoured attack aircraft.