"To the Chief of the GBTU TU 6th Department, Regional Engineer at the Kirov Factory
July 5th, 1943
I report on the experimental work performed at factory #100 during June of 1943.
The most attention was paid to Objects 237 (experimental IS tank) and 239 (KV-1S tank with an IS tank turret and 85 mm gun).
1. Object 237 (IS tank)
Assembly of the first Object 237 began on June 21st, 1943. Assembly was completed on June 30th, 1943. Assembly did not include installation of the turret, as it has not arrived.
The turret is being assembled at the Kirov factory.
On July 2nd, the tank traveled for 24 km for breaking in, showing defects in the tuning of the main friction clutch and planetary turning mechanisms.
The hull of a second tank was built at factory #200 on July 1st, 1943. Factory #100 began assembly of a second tank on July 3rd, 1943. Factory #200 is in the process of assembling a third hull.
2. Object 239 (modernized KV-1S tank with an IS tank turret and armament)
Work on converting the hull of KV-1S #15002 was finished at factory #200 on June 30th, 1943.
Presently, factory #100 has begun work on assembly of the tank. The turret is not completed. Delays in producing turrets for prototypes happen exclusively due to the management of the Kirov factory, which has distanced itself from this work and is at fault for failing to meet targets established by the GOKO.
3. On the armament of Objects 237 and 239
The factory received four 85 mm S-31 guns and one D-5 gun designed by factory #9 to arm the IS and modernized KV-1S experimental tanks.
The S-31 gun has a recoil length of 540 mm and a large bulky cradle, which makes it difficult to install into a tank.
The D-5 gun has a recoil length of 300 mm with a small and compact cradle, as well as a low loading axis. The ballistics of the guns are identical.
In addition, the D-5 gun can be converted to use the 122 mm caliber if the barrel and breech are replaced."