152 mm gun M1935 (Br-2)

Work on a long range 152 mm gun for Reserve of the Main Command units started in 1929, when the Bolshevik Plant in Saint Petersburg received from the Artillery Directorate requirements specifications for such a piece.[1] The project received a factory index B-10. First barrel was manufactured in April 1932; it was sent for trials even before the carriage, which had an unusual tracked construction, was ready. Development and testing of the B-10 continued until 1935; a number of problems were revealed, including slow elevation, low rate of fire and short service life. As a result, the gun was not adopted. The two produced barrels were experimentally modified for firing pre-rifled projectiles and polygonal projectiles respectively. The experiments didn't produce practical results. An attempt to improve elevation speed by use of an electric motor failed to provide smooth elevation. The Soviet Navy briefly considered adopting a derived weapon as a coastal gun, in towed or self-propelled variant, the latter based on T-28 medium tank chassis. Only the towed variant, B-25, reached factory trials; eventually it was canceled because of shortcomings of the design and decision of the Army not to adopt the B-10.[1]

Br-2, rear view.

In the early 1930s the Artillery Directorate ordered a development of a "heavy artillery triplex", consisting of a 152 mm gun, a 203 mm howitzer and a 280 mm mortar utilizing the same carriage. The Bolshevik Plant and the Barrikady Plant in Stalingrad were entrusted with the development. The 152 mm gun projects were called B-30 (sometimes referred to as B-10-2-30) and Br-2 respectively. Both mated a barrel ballistically identical to that of the B-10, to a tracked carriage of the 203 mm howitzer M1931 (B-4).

Late in 1936, the Bolshevik Plant delivered an experimental series of six pieces. A number of longer (55 calibres) barrels and a number of barrels with deeper rifling were manufactured. The B-30 barrels were also used for ultimately unsuccessful experiments with pre-rifled shells and with "Ansaldo system" variable depth rifling.

While generally similar to the competing design, the Br-2 had different barrel construction (built-up vs loose liner), slightly different breechblock and featured an equilibrating mechanism.

Despite results of trials, which favored the B-30, the Artillery Directorate decided to adopt the Br-2. The reasons for the decision are not clear. However, it was decided to switch to free tube barrel construction in production pieces, making the gun somewhat more similar to the B-30.

Although the Br-2 was adopted, it was evident that the gun had significant drawbacks. One of the problems was very short life of the barrel: it took about 100 shots for the muzzle velocity to drop 4%. In an attempt to tackle the problem, an experimental piece with longer (55 calibers) barrel was produced; another experimental barrel had smaller chamber and deeper rifling. The latter solution was eventually preferred and from 1938 a variant with deep rifling replaced the original barrel in production. It was claimed that the new variant had five times longer service life. However, service life of the new barrel was measured using different criterion (10% drop in muzzle velocity), so actual improvement was probably much smaller.[1]

Another drawback of the gun was its low mobility, aggravated by separate transportation of the barrel. Attempts to improve the tracked carriage (such as the experimental T-117, which was tried out in 1939) were ultimately unsuccessful. In 1938 the Artillery Directorate issued specifications for a wheeled carriage for the Br-2 and the 203 mm howitzer M1931 (B-4). The project was handled by the design bureau of Plant no. 172 (located in Perm), headed by F. F. Petrov. Because the design bureau was busy with other tasks, the development of the new carriage - factory index M-50 - advanced slowly; it never advanced past the design phase and was canceled after the outbreak of the German-Soviet War. An improved wheeled cart Br-15 for barrel transportation was considered in 1940 but was never adopted, because it couldn't improve the mobility of the carriage. It took until 1955 to develop a variant of the Br-2 - designated Br-2M - which had wheeled carriage and didn't require separate transportation.

The Br-2 was also used in a number of unsuccessful experiments with discarding sabot shells, intended to increase range. These included experiments carried out in 1940, with 162 mm barrel firing 162/100 mm shells. The barrel was damaged during the experiments; additionally, the gun was found to have unsatisfactory ballistics and problems with loading. Firing 152/107 mm shells failed to produce significant improvement in range.

The Br-19 was an experimental piece which combined elements of late production Br-2 (breechblock, barrel with deep rifling) with elements of B-30. The gun was tried out in 1939; it found superior to the Br-2 and was recommended for production, which, however, never started.[1]

The Br-21 was an experimental 180 mm gun developed privately at the Barrikady Plant by mating Br-2 barrel bored out to the 180 mm caliber to carriage of B-4. The gun reached trials on 20 December 1939. The gun turned out to be more powerful and accurate than the Br-2, but was never adopted, because of the need to produce a new ammunition.[1]

The Br-2 was in production from 1936 or 1937 to 1940. At least 37 pieces were manufactured. Early pieces had barrels with the original "shallow" rifling (at least seven, built in 1936–37), while late production pieces had barrels with the newer "deep" rifling (27 in 1939–40).