The main problem of the BAA-2 was the excessively complex form of the armored hull. It consisted of several large curved parts, the manufacture of which was a very difficult task. This led to the fact that the Izhora plant, already loaded with military orders, was unable to build a single serial armored car. However, the specialists of the enterprise took measures and proposed an alternative draft of the combat vehicle. It was distinguished from the unsuccessful BAA-2 using a simpler body with comparable characteristics.
Experienced armored car PB-4. Photo Oruzhie.info
The development of the new project, called PB-4, was carried out in the design office for special projects (KBS) of the plant under the guidance of N. Ya. Obukhov. A great contribution to the project was made by the design engineer Emmanuilov, the head of the Pomerantsev bureau and his deputy Grigoriev.
In the new project it was planned to use some developments on the BAA-2, however, it was necessary to introduce completely new solutions proposed by the results of tests of this machine. The main objective of the project was to simplify the design in terms of production technologies. In particular, to solve this problem, the armored parts of an existing BA-3 machine were used as the basis for the new hull. The power plant and chassis were borrowed from the Ford-Timken truck. As a result, the new PB-4 should have been different from the previous BAA-2, but still have similarities with other equipment.
In the project PB-4 for the first time in the domestic practice a welded bearing frame of frameless construction was proposed. The functions of the power elements were assigned to the armor, and all the main units were to be fixed directly on it. Most of the details of the hull and tower differed simplicity of form. All major parts had a thickness of 7 mm. The roof and bottom were slightly thinner - 4-5 mm. The tried-and-tested front-engine layout was maintained, with all other hull volumes being habitable.
The most notable difference between the PB-4 and the BAA-2 was the absence of side screens of complex shape. The power plant was placed inside the armored hood with a curved front wall and diverging sides. The bottom of the engine compartment was sealed. On top of the engine covered with a flat roof with a set of hatches for air access. Initially it was supposed to do only air cooling. Behind the hood there was an inclined frontal sheet of the habitable compartment with an inspection hatch and a machine-gun installation. At the level of the control compartment, the body had a relatively small width, after which its cross section increased. At the same time, its lower part retained its dimensions, and additional volumes were formed by the upper elements of the sides. The car received a horizontal roof with a turret and aft, consisting of several inclined parts.
Scheme of an armored car after one of the modifications. Figure Arms-expo.ru
On the roof of the building was located a tower based on the unit tank T-26. The dome was made of a cylindrical side and a round lid. In front of the tower was a rectangular embrasure for machine gun and cannon weapons. In the PB-4 project, they rejected the characteristic feed niche by installing a simple curved sheet instead.
On the sides of the hull, characteristic long wings were extended along the entire length of the vehicle. There were several mudguards under them. Over the wings placed additional floats. They were made in the form of long wooden beams of sufficient cross-section, upholstered with a thin metal sheet. Initially, the floats were long and fixed along the entire length of the board. They had almost no effect on the level of protection of the sides, but allowed to increase the displacement, and with it the characteristics of the machine on the water. Inside the case was a hand-operated pump for pumping water. In the bottom there were plugs for draining water.
Under the hood was placed the carburetor engine "GAZ-A" power 40 hp Through a four-speed manual gearbox, torque was given to the drive shaft, which provided the drive for the two rear axles. Since the elements of the chassis were outside the hermetic housing, the shaft went out through a special gland. Worm gears and bevel differentials were used on driving axles.
The drive shaft of the rear axles reached the stern of the hull, where a propeller was installed on it. As in the case of BAA-2, the power flow gap was not envisaged. When driving over land and water, the wheels and the screw always rotated simultaneously.
Modified version of the machine. In particular, the length of the floats is reduced. Photo Oruzhie.info
The undercarriage with the wheel formula 6х4 was built on the basis of a dependent suspension. All bridges were fixed in small niches of the hull. The front axle was completed with longitudinal semi-elliptical springs. Two rear axles with the help of similar shock absorbers were assembled into a kind of truck. Rear wheels got a double busbar. The armored car was equipped with a pair of spare wheels. Nodes for their suspension were behind the front axle, with a certain excess above it. When driving on rough terrain, the spare wheels increased the permeability, preventing the car from dropping to the bottom. The wheels of the rear axles could be equipped with Overall tracked belts.
The main weapon of the prospective armored car was the 45-mm rifled 20K gun. In the laying of the fighting compartment housed ammunition in the form of 52 shells. On one installation with a gun was a twin machine gun DT. Direct the tower weapon It was proposed using a telescopic sight TOP and periscopic TP-1. The turret had manual pickup drives. Another machine gun was placed in the front hull sheet, on the starboard side. Unlike the tower, he could fire only part of the front hemisphere. The total ammunition of two machine guns consisted of 2268 cartridges in 36 stores.
The crew of the armored vehicle PB-4 consisted of four people. The driver and the gunner were in front of the habitable compartment, a hatch was provided above their places in the roof of the hull. The driver could follow the road with a viewing hatch in the front plate, covered by a flap with a slit. The arrow was asked to observe with a machine gun. Two other crew members were in the tower. They fell into place through the hatches in the roof. Along the perimeter of the tower there were slots and triplexes for observation.
In terms of size and weight, the new floating PB-4 hardly differed from other equipment of its class. The length of the vehicle reached 5,3 m, width less than 2 m, height 2,25 m. Combat weight 5,28 T. The estimated speed on the highway reached 50 km / h, on the water up to 3-5 km / h. Automotive chassis allowed to overcome some obstacles, but the lack of all-wheel drive limited the real maneuverability.
Back view. Photo Oruzhie.info
Already in September, the Izhora Plant completed the 1933 of the year and put three experienced armored vehicles of the new model to the test. Checks started in October and lasted several weeks. During this time, it was found that in its current form, armored cars have a lot of problems and cannot be accepted for service. The army commission accepted the armored vehicles conditionally, and the Red Army’s Department of Mechanization and Motorization refused to pay for their production until acceptable results were obtained.
In practice, it was found that the welded bodies were assembled poorly, and water entered the machines through the remaining gaps. At the same time, in general, the machines kept up well, although they could not reach high speed. Road performance on the highway was satisfactory, but on rough terrain, characteristics dropped sharply. In addition, due to insufficient ventilation of the hood, the engine overheated, and also heated the air in the habitable compartment. The turret of the T-26 without a niche turned out to be unbalanced, which made it difficult for the horizontal guidance.
In December, the KBS Izhora plant's 1933 year finalized the draft PB-4 to reflect the test results. A new version of it suited the customer, and at the beginning of the next year, an agreement for the assembly of 10 pre-production machines appeared. In March, the first three armored cars set off for testing, and the construction of the rest was postponed to the near future. It was found that some of the problems managed to get rid of, but others remained. First of all, engine overheating persisted. However, the cars did not begin to be altered, and soon they were sent to run along the route Kolpino-Moscow.
In the summer of the same year, the available experimental machines were refined. Taking into account the accumulated experience, they changed the design of the shock absorbers, improved the ergonomics of workplaces and introduced other changes. In addition, the machines have mounted different engine cooling systems. In particular, radiators of increased capacity and a special heat exchanger on the bottom, interacting with seawater, were tested. To improve cooling on land, the front hull sheet was equipped with a hatch with a movable pressure cap.
In September 1934, prototypes with different configurations underwent comparative tests. The machine with an additional heat exchanger performed best. Soon, four experienced armored vehicles received such equipment. However, even after this, the conditions inside the case left much to be desired. The air temperature inside the habitable compartment constantly exceeded 40 ° C.
After the next modifications, the experimental equipment again came to the test. At the same time, since the spring of 1935, only five of the six armored vehicles were operating at the test sites. One of them was dismantled, and soon transferred to the test by shelling. Others continued testing, both in the Kolpina area and in the Kubinka town near Moscow. From a certain time, PB-4 were studied in parallel with experienced BA-3 and compared with each other. It turned out that the floating armored car has only one advantage over its competitor.
According to the results of several consecutive improvements, experienced PB-4 armored cars showed good performance on land. Patency was now satisfactory, and according to these indicators, the armored cars hardly differed from other equipment of their class. At the same time, they had an advantage in the form of the possibility of swimming, but they failed to realize all such advantages.
On the water, armored cars dispersed only to 1-1,2 km / h. During a special test, the speed of 2,8 km / h was developed, but this was ruled out in a combat situation. In addition, the cars were extremely unstable on the water. The turn of the tower led to a noticeable roll. In some circumstances, the gun barrel could even fall into the water. Water was still being drawn into the hull, and because of an insufficiently effective pump, it had to be drained ashore. At the same time, traffic jams in the bottom opened only from the outside.
Attempts to improve the design of an armored car for a long time. In August 1935, the last water tests took place. A certain increase in characteristics was obtained, but in general the equipment still did not suit the customer.
According to the results of all tests and refinements, the Office of Mechanization and Motorization decided to abandon the armored vehicles PB-4. On land, they almost did not differ from the BA-3 type cars, and the characteristics on the water were far from the desired ones. Moreover, practice has shown the senselessness of new attempts to improve the design. In fact, PB-4 turned out to be an unsuccessful copy of another machine with dubious differences that have no practical value. The project should be closed.
By this time, six experienced armored cars were built. One of them was dismantled in the spring of 1935, and then experienced shelling. Obviously, soon the broken hull went to the smelter. Three cars were sent for storage, another was listed as part of the armored forces of the Moscow Military District. The sixth remained in Kubinka. In the future, four armored vehicles under certain circumstances ceased to exist. Only one sample, previously sent to Kubinka, has been preserved. Now he is an exhibit of the museum of armored vehicles.
Projects BAA-2 and PB-4 failed. Despite all the efforts, the Soviet designers did not manage to create a floating armored car with acceptable characteristics. But the army still showed interest in such a technique, which soon led to the launch of a new project. In 1936, the Izhora plant developed another machine of this kind, known as PB-7.
Solyankin A. G., Pavlov M. V., Pavlov I. V., Zheltov I. G. Domestic armored vehicles. XX century. - M .: Exprint, 2002. - T. 1. 1905 – 1941.
Kolomiets M.V. Armor on wheels. History Soviet armored car 1925-1945's. - M .: Yauza, Strategy KM, Eksmo, 2007.