2. The fuel tanks may be located on the bottom of the fighting compartment to increase the amount of ammunition that can be carried and its convenient placement.
3. The twin 76 mm guns must be capable of firing salvos and firing separately.
4. The rate of fire during salvo firing (number of salvos per minute) must be close to that of the KV-1; when both guns are fired separately (one at a time) the rate of fire must exceed that of the KV-1 by 70–80%.
VIII. The tank’s mobility, engine, suspension, and communications equipment must be similar to that of the KV-1.
Note: the factory may alter and supplement this operational requirement to improve the design in coordination with the People’s Defense Commissariat, the Armor Directorate of the Red Army, and the People’s Commissariat of the Tank Industry.{6}
As was the case with the gun system for the first version of the KV-7, work on the twin ZIS-5 76 mm guns was assigned to the Ural Heavy Machinery Plant. The project was overseen by L. I. Gorlitsky (on drawings, he is identified as the chief designer), and N. V. Kurin and G. F. Ksyunin worked on the system that was assigned the factory designation U-14. Judging by the dates listed on the drawings of individual parts, design work began not later than January 25, 1942; that is, before the operational requirement for the upgraded KV-7 was issued. Design work on the U-14 lasted until mid-February, and work to manufacture the upgraded KV-7 began in the second half of that month. The assault tank was not built from scratch: the existing KV-7 with the U-13 system was modified. The superstructure itself did not need to be altered; the changes affected only the mantlet and the ammunition storage rack.
The test program for the upgraded KV-7 was drafted by March 7, 1942. In addition to the firing trials during which 400 rounds were to be fired, it was proposed that the vehicle be driven a total of 50 kilometers. However, the tests had to be postponed because the Chelyabinsk Kirov Factory was occupied with other projects at the time. As a result, the firing trials were held much later, and no mobility test was performed. Kirov Factory chief designer, Maj. Gen. Zh. Ya. Kotin was given the following report about the tests conducted on May 16, 1942:
Assembly of the KV-7 tank was completed on May 11, 1942, and on the 14th it underwent preliminary testing at the Kopeysk Test Range. Seventeen highexplosive fragmentation shells were fired from both systems, 5 by individual fire and 12 in salvos. A 1.5 X 1.5 meter target at a range of 800 meters was used.
The following preliminary conclusion can be drawn from the data:
1. The accuracy of the twin systems in firing from a halt is good. After zeroing, 11 rounds fell in an ellipse with a long axis of 40 meters and the short axis of 3 meters.
2. The rate of fire was 6–7 salvos per minute. Due to system imbalance and the self-braking elevation mechanism—a sector-type (elevation) mechanism mounted on the twin guns—the elevation angle increased spontaneously by 25 mils after each salvo.
3. The twin gun traversing mechanism requires both hands to operate, which is completely unacceptable.
4. The placement of shell cases in an inset in the turret causes great difficulty during operation and cannot be accepted. Open storage must be used.
5. The effort required to operate the twin gun trigger mechanism during salvo firing is too great and must be cut at least in half.
6. No retraction device is provided for the twin guns; the rear wall of the turret must be adapted for that purpose, simultaneously making it an entryway for the crew.{7}
According to development plans at Experimental Tank Plant No. 100 of the People’s Commissariat of the Tank Industry (located in Chelyabinsk), which had been established in March 1942, the upgraded KV-7 was to undergo factory tests from June 1 through 10, followed by state testing. That did not take place: interest in an assault tank had waned, and Factory No. 100 was fully engaged in developing the KV-1S. That meant other development projects had to be postponed. The main reason the KV-7 project stopped was that design work to install the ML-20 152 mm gun howitzer in it was in full swing by June 1942.
The assault tank story might have ended here, but work on it did not cease. The KV-7 came up again in October 1942. P. F. Solomonov (a major at the time) inspected the SP gun during a business trip to the Kirov Factory. At Solomonov’s insistence, the KV-7 was taken for a 15-kilometer test run. Firing trials could not be conducted because the traversing mechanism was malfunctioning. On November 10, Kotin received a letter from the chief of the GAU’s Artillery Committee, Col. Gen. V. I. Khokhlov, that read as follows:
The Kirov Factory of the People’s Commissariat of the Tank Industry of the USSR has built a KV-7 tank with a non-rotating prismatic turret and twin ZIS-5 76 mm tank guns installed. After undergoing factory tests, the tank remains at the experimental factory of the People’s Commissariat of the Tank Industry, and no decisions have been made concerning it.
It is the opinion of the Artillery Committee that this system should be sent for proving-ground tests and troop trials.
The troop trials should be performed under actual combat conditions, and the proving-ground tests should be done at the Tagil Test Range of the People’s Commissariat of Munitions of the USSR.
The following actions must be taken before the KV-7 is sent for testing:
1. Install a commander’s observation cupola.
2. Inspect and repair the transmission, powerplant, and running gear.
3. Check the artillery system and repair and adjust the laying devices (elevation and traverse).
4. Adjust the trigger mechanisms
5. Modify the spent case catcher for greater convenience in loading.
If you agree, please task Factory No. 100 of the People’s Commissariat of the Tank Industry to perform the necessary work and provide a crew for the tank.{8}
The KV-7 was neither upgraded, nor did it undergo troop trials. S. A. Afonin, chief of the GABTU’s Armor Directorate, felt that it made no sense to upgrade the tank, which had undergone a number of tests by December 10, 1942, because it had failed to fire a synchronous salvo. Also, instead of pairing the ZIS-5 76 mm guns, a single gun of a much larger caliber should be mounted, which Factory No. 100 was currently engaged in doing. However, work on the KV-7 project did not end there.
Decrees No. 12016ss and 12017ss issued on June 27, 1942, by the People’s Council of Commissars of the USSR tasked the Saratov Gear-Cutting Machinery Plant to manufacture prototypes of a planetary transmission. A team led by G. I. Zaichik at the Bauman Institute of Mechanical Engineering in Moscow developed this transmission. Manufacture of the transmission was delayed: instead of August, two prototypes were made in December 1942, and they arrived at Factory No. 100 on the 30th. A team of designers from the Bauman Institute arrived in Chelyabinsk on January 2 to supervise the installation. The KV-7 was selected as the tank for use in testing the planetary transmission. Installation of the new transmission was delayed because Factory No. 100 was occupied with other projects. Instead of January 16 as instructed by I. M. Zaltsman, People’s Commissar of the Tank Industry, the installation was completed only on February 17. It is possible that the delay at this stage was deliberate, because a different transmission had been undergoing testing on KV-1S No. 15002 since November 19, 1942—one designed by Eng. Col. A. I. Blagonravov.