The first prototype flew in 1953 and was very successful except when it fired its guns, as their combustion gasses disturbed the airflow into the engines and caused them to flameout or hiccup.

Remedying this problem took over a year and involved the radical change of moving the engine air intakes all the way to the very front of the aircraft and repositioning the guns from the tip of the nose to the bottom of the fuselage, just behind the nosewheel.

Only five production aircraft had been completed before the entire program was canceled in early 1956 when the VVS discarded its close air-support doctrine in favor of tactical nuclear weapons on the battlefield.

As was traditional for Ilyushin ground-attack aircraft, the core of Il-40's structure was a load-bearing armored shell that protected both crew positions, six fuel tanks and part of the radio and electrical equipment.

[2] The initial armament was six 23 mm (0.91 in) Nudelman-Rikhter NR-23 autocannon mounted in the nose, three on each side, each with 150 rounds, with their muzzles protruding into the slipstream.

During the first aerial test of the cannons at the end of March 1953 the muzzle flash temporarily blinded the pilot and both engines flamed out.

One problem occurred almost immediately during testing when the blast gases accumulated in the section where spent cartridges and links were saved and sometimes ignited.

The tests were generally successful with the Il-40 proving to be easy to fly, maneuverable enough to be a handful for the MiG-15bis and MiG-17 fighters opposing it and considerably superior to the piston-engined Ilyushin Il-10M ground-attack aircraft then in service.

[2] The change in position of the guns and the extension of the air intakes, which looked "uncannily like a double-barreled shotgun,"[2] allowed the nosewheel to be moved forward to lengthen the wheelbase.

[2] Ilyushin began construction of another prototype to evaluate this solution and this was endorsed on 16 October 1954 when the Council of Ministers ordered production to begin at Factory (Zavod) No.

[2] Five of these had been completed by the spring of 1956 and were undergoing preflight tests when the entire program was canceled on 13 April 1956 and all components in preparation scrapped.

The second variant was a torpedo-carrying version called the Il-40T which was based on the fuselage of the Il-40K, but the navigator-bombardier's position had optically flat glass panels to facilitate aiming.