With the outbreak of the Great Patriotic War, there was an urgent need for a spotter aircraft to pinpoint artillery fire. In the initial stage of the war, the job was done by modified Su-2 aeroplanes, and starting in mid-1943, by Il-2 attack aircraft. It was obvious that those machines were not suitable for pinpointing shellfire and a dedicated aircraft was needed. In July 1943, the AFRA Scientific Research Institute developed a PR for a tactical recon and artillery fire observation aircraft under the 1943-44 aircraft prototype engineering plan.
By November 1943, the design bureau of O.P. Sukhoi completed the design for a three-seat spotter plane with two M-62 engines based on Germany's FW-189 recon plane. The spotter aeroplane was incorporated into the PCAI 1944-45 aircraft prototype engineering plan, but in the course of the plan's coordination and approval the project was scrapped.
It was not until after an energetic intervention on the part of Chief Marshall of Artillery N.N. Voronov that the aircraft was restored to the programme. On 10th July the USSR CM passed a resolution to build an experimental prototype of a recon and spotter aircraft, which committed P.O. Sukhoi to designing and building the aircraft with two ASh-83 engines in two prototypes, the first one to be made available for Governmental Tests by 15th September 1947.
The aircraft's conceptual design was ready in June 1946, but the PRs were not produced by the Scientific Research Institute of Air Forces until late October, with a mock-up of the aeroplane submitted to the commission as late as March as a result. In the course of the mock-up review, a number of comments were voiced, one of them calling for the aircraft crew to be expanded up to four.
An 11th March 1947 resolution of the USSR CM approved the 1947 aircraft prototype engineering plan, with Sukhoi Design Bureau's assigned the artillery recon/spotter with two ASh-82M engines carried and with upgraded specifications.
The Su-12 aircraft was built in August 1947, but despite on-going supervision on the part of N.N. Voronov, the armaments and certain types of equipment failed to arrive as planned. P.O. Sukhoi made the decision to conduct the manufacturer's flight tests without complete equipment onboard, the missing components to be installed as they arrived.
On 26th August 1947, the plant's test pilot N.D. Fikson took the Su-12 up for its maiden flight. The manufacturer's flight tests were completed on 30th October 1947. In the course of the manufacturer's tests, due to the underperformance of the ASh-82M engines (2,200hp), they were replaced with ASh-82FN (1,850hp), resulting in a failure to meet the aircraft's top speed and ceiling requirements imposed by government resolution.
On 20th December 1947, the Su-12 aeroplane (without weapons) was officially handed over for governmental tests, which confirmed the findings of the manufacturer's flight tests in their entirety. The test report pointed out a number of faults and shortcomings to be eliminated during production. The test report specifically provided for repeat governmental tests with armaments onboard prior to putting the aircraft into production.
In June 1948, the Governmental Test Report on the Su-12 aircraft and a draft of a relevant USSR CM resolution to put the aircraft into service and production at plant No 381 was submitted at a higher level. Due to a variety of reasons, the approval was not ready till November, the paperwork left waiting for an official approval; in the meantime, the Design Bureau (plant No 134) was instructed to install the armaments and remedy the shortcomings listed in the Governmental Test Report.
To get to the root of the shortcomings, early in 1949 the aeroplane was subjected to additional flight tests at the plant, their findings leading to a number of modifications, followed by repeated official tests in the period between July and September 1949, which finally culminated in the aeroplane's being recommended for introduction into service.
In October 1949, the documentation package was resubmitted to the government for review, with a proposal to set up production of Su-12 aircraft at a plant in Czechoslovakia, the facilities in this country said to have no production capacity to spare. The paperwork submitted was returned, its approval withheld, the reasons citing failure of the characteristics achieved to comply with the specifications laid down by the government's decree of 11th March 1947.
All the subsequent attempts of P.O. Sukhoi to get clear-cut directives on the Su-12 project met with failure.