The 150-ton “Field Monitor” project had a number of the most serious flaws. First of all, the proposed combat vehicle — differing in powerful defense and serious armament — had unreasonably large dimensions and weight. This would complicate the construction and operation of equipment. In addition, there were grounds for doubting the reliability of the proposed steam power plant. In 1916, the army, having familiarized with the project, refused its support. For the next few years, Holt tried to improve the previously proposed machine and improve its basic characteristics.
Holt Steam Wheel Tank Prototype, Front View
Despite the failure of the military, the development of original ideas was continued. At the same time, it took the path of reducing the size and weight of the machine. A large super-heavy model could hardly justify itself, and therefore a new combat vehicle was proposed to be made smaller. Among other things, this allowed the use of a significant number of already existing units and assemblies borrowed from serial equipment.
The new project was launched at the end of 1916. By this time, the designers of Holt had time to get acquainted with the available information about the latest foreign tanks and the features of their combat use. Perhaps, in their new project, they used some ideas and solutions, spied on by foreign colleagues. In addition, the name of a new class of combat vehicles was borrowed from British combat vehicles. The promising model has received several names. It is known as the Holt Steam Tank, 3 Whelled Tank, etc. A little later, together with the support of the army, the project received a new name - Steam Wheel Tank ("Steam wheel tank").
The Holt Steam Wheel Tank project proposed the construction of a three-wheeled armored vehicle equipped with a steam power plant. Depending on the wishes of the customer, she could carry a cannon or machine-gun armament. Despite the use of some ideas from the previous project, the promising steam tank should have been three times shorter and nine times lighter. Reducing the size and weight could also lead to a certain reduction in firepower due to the impossibility of using a weapon system as part of several 152-mm guns.
Protection of the crew and internal units were assigned to armor steel. Interestingly, in the design of the future wheeled tank applied the principles of differentiated booking. So, the front and front parts of the hull should have an 0,63 inch thickness (16 mm), and the stern should have been made from 5,8-mm (0,23 inch) parts. Separate armor plates of relatively simple forms had to be fastened to the frame with the help of rivets.
An original form of the hull was developed, allowing the distribution of internal volumes between weapons, people and steam engine. The frontal part of the body had a rectangular shape, and instead of the front sheet was used grille with vertical slits, necessary for cooling the power plant. Behind the front sheet there was a large box-shaped case, the cross section of which did not change until the feed unit. The latter was proposed to be made from a pair of beveled sheets and one vertical central one.
At the front of the hull an additional support was fixed, which is necessary for installing the roller-wheel. It was a triangular in terms of the unit with a rounded front top. Due to the large mass of the machine, the roller bearing removed was characterized by high strength and was made in the form of a reinforced system of sheet metal, profiles and other parts.
In the stern of the hull it was proposed to mount a superstructure-cabin that contained the fighting compartment. Its stern sheet, equipped with an embrasure of the main gun, was a continuation of the vertical part of the main body. On the sides of it were oblique zygomatic sheets, with the help of which the front part of large niches above the wheels was formed. The central part of the superstructure had a maximum width and was equipped with vertical rectangular sides. Behind it was another pair of beveled sheets connected to a vertical frontal part. The central element of the roof of the superstructure was located horizontally, while the front and rear were proposed to be tilted in different directions.
The specific choice of the power plant led to the need to use a non-standard hull layout. The superstructure, as well as part of the volumes under and in front of it, served as a fighting compartment. Below the fighting compartment, steam engines with a mechanical transmission were installed that connected them with driving wheels. The boiler was placed in front of the hull, just behind the frontal grille. The dense layout of the power plant units eliminated the need for long pipelines.
The power plant for the Steam Wheel Tank was developed jointly by Holt and Doble. Previously, such cooperation had led to the creation of several steam tractors, and now the existing experience was used in designing a combat armored vehicle. In the "tank" steam engine used some serial units, while other devices had to be finalized or created from scratch.
Frontal projection of the "steam wheel tank"
In front of the hull were two steam boilers operating on kerosene. Liquid fuel from its own tank was supplied to the burners and heated the water to the desired temperature. In front of the boilers were condensers for cooling the exhaust steam. These devices were equipped with steam driven fans. For servicing the boilers, the hull roof had a hatch with hinged lids. Combustion products were discharged through the exhaust pipe, which was located behind this hatch.
Each boiler was associated with its own piston machine. Machines were made in the form of separate units and placed horizontally below the combat compartment. Each car had two cylinders attached to a common frame. Each such engine developed the power of the 75 HP. With the help of a simple transmission, the engine torque was delivered directly to the axles of the driving wheels. The control system made it possible to control the steam supply and parameters of the transmission, changing the main characteristics of the tank as required.
A running gear was used, similar to those used in the tractor projects of that time. So, in the aft hull on a rigid suspension without depreciation it was proposed to install a pair of large and wide wheels. Their rims were made of metal and had developed V-shaped lugs. For management it was proposed to use the original front wheel-roller. On the support brought forward, a swivel base with a U-shaped frame for the roller was placed. The rink itself consisted of three parts: cylindrical central and side, made in the form of truncated cones with rounded edges. Three parts were mounted on a common axis, which was mounted on the frame. Management at the rate it was proposed to carry out with the help of mechanisms that turn the roller around a vertical axis.
For a slight increase in maneuverability and the ability to climb obstacles, the Steam Wheel Tank received an inclined support plate placed in front of the roller on special beams. With its help, the tank could rely on the obstacle, after which the thrust of the driving wheels had to push the front roller onto it.
View of the stern
Holt's steam tank was to receive advanced cannon and machine gun weapons. There are at least two options for placing artillery and rifle systems. The first of these involved the use of an 75-mm mountain howitzer of one of the existing types. This tool should be mounted on the installation of the chopping sheet. In the side sheets of the superstructure there were installations for two rifle-caliber machine guns.
According to other sources, the armored vehicle’s weapons should have included two six-pound (57 mm) cannons, as well as two machine guns. The guns could be placed on the installations of the stern sheet, whereas onboard units were intended for machine guns. According to available data, the project Steam Wheel Tank provided for the use of just such an armament complex. Another option, which suggested the installation of an 75-mm howitzer, either did not go beyond the preliminary design stage, or was the result of some later error.
The main armament of the armored vehicle was placed on the aft installation. Thus, she had to go into battle in reverse. At the same time, the specificity of the control systems and the undercarriage eliminated the rapid transfer of fire to large angles, which required a smooth turn of the entire tank. While on the march, the barrel or gun barrels were turned back, increasing the overall envelope of the car.
The crew of the future tank consisted of six people. One of them served as a driver; the rest were to serve artillery and small arms. To observe the road the driver was asked to use a small hatch in the front of the cabin. Other crew members could search for targets using several other hatches in other armor plates, as well as with the help of standard weapon embrasures. Access to a single manned tank compartment was provided by a hatch in the roof of the superstructure.
Boiler steam armored vehicle
Outwardly promising steam tank was like a tractor. The dimensions of the car also forced to recall a similar technique of the time. The length of the “Three-wheeled steam tank” was 6,87 m with a width slightly more than 3 m and height about 3 m. The combat weight was 17 t. According to calculations, the armored car could even develop a small speed, not higher than 8-10 km / h. At the same time, it was supposed to obtain sufficient mobility on rough terrain. However, as it turned out during the tests, such plans were never fulfilled.
The development of the Holt Steam Wheel Tank project began at the end of 1916 and lasted several months. After that, the construction of an experimental armored car started, which took a lot of time. The finished prototype tank with a steam engine was removed from the assembly shop only in February 1918 of the year. A few weeks later he was sent to the Aberdeen Proving Ground for testing.
During one of the first tests, the steam tank went onto the track of the landfill and passed just 50 feet (15 m), and then got stuck. According to common, but not quite correct information, the tests were stopped at that. However, in fact, the checks were resumed, and in just a few minutes. During this time, the boilers gained the desired temperature and created the required pressure in the cylinders. Out on the desired characteristics, armored car without significant problems got out of the mud and continued to move.
Tests continued until May 1918, and allowed to establish the real possibilities of an unusual combat vehicle. After reviewing the prototype at the site, as well as examining its characteristics, the US military made all the necessary conclusions. The Holt Manufacturing Company steam tank was considered unsuccessful and unsuitable for adoption. The project should have been closed as unnecessary.
As far as is known, after the tests that led to the refusal of the military, the development company did not try to develop the existing project and improve the performance of the combat vehicle. Instead of restructuring and improvement, an interesting sample was sent to storage. Later he was dismantled for metal. It is possible that some units of the steam engine, which did not have time to develop a resource, could continue to work as part of other serial-type machines.
The Holt wheeled steam tank project failed. The original prototype combat vehicle could not show itself in a good way, which led to an understandable result. The negative decision of a potential customer was associated with a number of characteristic features of the machine offered to him. It can be assumed that the further development of the existing project could not lead to getting rid of the existing shortcomings and obtaining the desired opportunities.
As follows from the available data, the main claims to the Steam Wheel Tank tank concerned insufficient mobility and maneuverability, which was demonstrated already during the first test drive to the landfill. Having developed the required vapor pressure, the existing power plant showed acceptable performance, but the power density was no more than 9 hp. per ton imposed certain restrictions on the overall mobility characteristics. The second factor that had a negative impact on the mobility of the tank was the wheeled chassis. Despite the use of the widest wheels, the pressure on the bearing surface was too great and provoked bury on soft soils.
Steam Engine Diagram
The proposed complex of cannon weapons, in general, looked satisfactory. At the same time, the limited targeting angles of cannons and machine guns, as well as the distribution of weapons in different sectors, could be considered flaws. Also on the fighting qualities negative impact of the inability to transfer fire to a large angle without turning the whole car, hampered by the use of an imperfect steering system with a swivel roller.
However, it must be admitted that the designers of Holt, who had previously developed the 150-ton Field Monitor, took their mistakes into account, and therefore the new Steam Wheel Tank project was more successful. First of all, the authors of the new project abandoned the idea of increasing the size and use of several large-caliber guns. All this made it possible to optimize other aspects of the design, as well as to simplify the future construction of a prototype.
However, at the heart of the new steam tank project were not the most successful ideas, which led to the natural sad ending. During short trials, the only prototype built failed to show high performance, and therefore did not go into the series, and later went on to disassemble. Experienced to identify another armored combat vehicle scheme, which should not be used to create new military equipment.
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