In 1915, the American company Holt Manufacturing proposed the original project of a super-heavy armored combat vehicle with powerful cannon and machine gun armament. Self-propelled wheeled vehicle 150 ton Field Monitor was intended for use in the southern borders of the country to protect against attacks by Mexican armed formations. However, the proposed project did not interest the army. The development company tried to improve the existing project, as well as develop a new armored vehicle for a similar purpose. This project remained in history under the name Holt Steam Wheel Tank.
The 150-ton "Field Monitor" project had some of the most serious flaws. First of all, the proposed combat vehicle - featuring powerful protection and serious armament - had unreasonably large dimensions and weight. This would complicate the construction and operation of equipment. In addition, there was reason to doubt the reliability of the proposed steam power plant. In 1916, the army, having familiarized itself with the project, refused to support it. Over the next several years, Holt tried to improve the previously proposed machine and increase its main characteristics.
Prototype Holt Steam Wheel Tank, front view
Despite the refusal of the military, the development of the original ideas 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 the new combat vehicle was proposed to be made smaller. Among other things, this made it possible to use a significant number of already existing components and assemblies borrowed from serial equipment.
The new project was launched at the end of 1916. By this time, Holt's designers had time to familiarize themselves 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, peeped from foreign colleagues. In addition, the name of the new class of combat vehicles was borrowed from the 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, it could carry cannon or machine-gun armament. Despite the use of some of the ideas of the previous project, a promising steam tank was supposed to have three times the length and be nine times lighter. Reducing the size and weight could also lead to a certain decrease in firepower due to the impossibility of using a complex of weapons as part of several 152-mm guns.
Scheme of the car, view on the starboard side
The protection of the crew and internal units was assigned to armored steel. Interestingly, the principles of differentiated booking were used in the design of the future wheeled tank. So, the frontal and front hull parts should have a thickness of 0.63 inches (16 mm), and the stern should be made from 5.8 mm (0.23 inches) parts. Separate armor plates of relatively simple shapes were to be riveted to the frame.
The original shape of the body was developed, which made it possible to distribute the internal volumes between weapons, people and a steam engine. The frontal part of the hull had a rectangular shape, and instead of the front sheet, a grill with vertical slots was used, which was necessary for cooling the power plant. Behind the frontal sheet there was a large box-shaped hull, 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.
An additional support was fixed on the front of the hull, which was necessary to install the roller-wheel. It was a triangular unit with a rounded front apex. Due to the large mass of the machine, the carried roller support was distinguished by high strength and was made in the form of a reinforced system of sheet metal, profiles and other parts.
View from above
In the aft part of the hull, it was proposed to mount a superstructure-wheelhouse that could accommodate 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 there were beveled cheekbones, with the help of which the front part of the 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 superstructure roof 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 were placed with a mechanical transmission that connected them to the drive wheels. The boiler was placed in the front of the hull, just behind the front grille. The dense layout of the power plant units made it possible to do without long pipelines.
The power plant for the Steam Wheel Tank was developed jointly by Holt and Doble. Previously, such cooperation managed to lead to the creation of several steam tractors, and now the existing experience was used in the design of an armored combat vehicle. In the "tank" steam engine, some serial units were used, while other devices had to be modified or created from scratch.
Frontal projection "Wheeled steam tank"
In front of the hull there were two steam boilers running on kerosene. Liquid fuel from its own tank was fed to the burners and heated the water to the required temperatures. In front of the boilers, there were condensers for cooling the waste steam. These devices were equipped with steam driven fans. To service the boilers, the roof of the hull had a hatch with hinged covers. Combustion products were removed through an exhaust pipe located behind this hatch.
Each boiler was connected to its own piston machine. The vehicles were made in the form of separate units and were placed horizontally below the fighting compartment. Each machine had two cylinders mounted on a common frame. Each such engine developed 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 the parameters of the transmission, changing the main characteristics of the tank as required.
A chassis was used, similar to those used in the projects of tractors of that time. So, in the aft part of the hull on a rigid suspension without shock absorption, 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 control, it was proposed to use the original front wheel-roller. A swivel base with a U-shaped frame for the roller was placed on the forward support. The roller itself consisted of three parts: a cylindrical central and lateral, made in the form of truncated cones with rounded edges. Three parts were mounted on a common axle, which was mounted on the frame. It was proposed to control the course using mechanisms that rotate the roller around a vertical axis.
To slightly increase the cross-country ability and provide the ability to climb obstacles, the Steam Wheel Tank received an inclined support plate, carried out in front of the roller on special beams. With its help, the tank could lean on an obstacle, after which the traction of the driving wheels had to push the front roller onto it.
Stern view
Holt's steam tank was supposed to receive a developed cannon and machine gun armament. At least two variants of the placement of artillery and rifle systems are known. The first of them involved the use of a 75-mm mountain howitzer of one of the existing types. This tool should have been mounted on the installation of the stern sheet of the felling. In the side sheets of the superstructure, there were installations for two rifle-caliber machine guns.
According to other sources, the armament of the armored vehicle was supposed to include two six-pound (57 mm) cannons, as well as two machine guns. The guns could be placed on the installations of the stern sheet, while the onboard units were intended for machine guns. According to the available data, the Steam Wheel Tank project provided for the use of just such a complex of weapons. Another option, which proposed the installation of a 75 mm howitzer, either did not leave the preliminary study stage, or is the result of some later mistake.
The main armament of the armored vehicle was placed on the stern installation. Thus, in battle, she had to go in reverse. At the same time, the specificity of the control systems and the chassis excluded the rapid transfer of fire to large angles, which required a smooth turn of the entire tank. While moving on the march, the barrel or the barrels of the guns turned out to be turned back, increasing the overall dimensions of the vehicle.
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 monitor the road, the driver was asked to use a small hatch in the frontal leaf of the cabin. Other crew members could search for targets using several other hatches in other armor plates, as well as using standard weapon embrasures. Access to the single habitable compartment of the tank was provided by a hatch in the superstructure roof.
Steam armored vehicle boiler
Outwardly, a promising steam tank looked like a tractor. The dimensions of the car also made us remember a similar technique of that time. The length of the "Three-wheeled steam tank" was 6, 87 m with a width of slightly more than 3 m and a height of about 3 m. Combat weight was 17 tons. According to calculations, an armored vehicle, even on a good road, could reach a low speed, no higher than 8-10 km / h … At the same time, it was supposed to get sufficient mobility on rough terrain. However, as it turned out during the tests, such plans were never implemented.
Development of the Holt Steam Wheel Tank project began at the end of 1916 and lasted for several months. After that, the construction of an experimental armored vehicle began, which took a lot of time. The finished prototype of the tank with a steam engine was withdrawn from the assembly shop only in February 1918. A few weeks later, he was sent to the Aberdeen Proving Ground for testing.
During one of the first tests, the steam tank entered the landfill track and walked only 50 feet (15 m), after which it got stuck. According to widespread, but not entirely correct information, the tests were stopped at this. However, in fact, the checks resumed, and only a few minutes later. During this time, the boilers reached the required temperature and created the required pressure in the cylinders. Having reached the required characteristics, the armored vehicle got out of the mud without significant problems and continued to move.
The tests continued until May 1918 and made it possible to establish the real capabilities of the unusual combat vehicle. After reviewing the prototype at the test site, as well as studying its characteristics, the US military made all the necessary conclusions. The Holt Manufacturing Company steam tank was considered unsuccessful and unusable. The project should have been closed as unnecessary.
Steam engine
As far as is known, after the tests that led to the failure of the military, the development company did not try to develop the existing project and improve the characteristics of the combat vehicle. Instead of rebuilding and improving, the most interesting sample was sent for storage. Later it was dismantled for metal. It is possible that some units of the steam engine, which did not have time to develop their resource, were able to continue working as part of other machines of serial types.
The Holt wheeled steam tank project ended in failure. The original prototype of the combat vehicle could not show itself in a good way, which led to an understandable result. The negative decision of the potential customer was associated with a number of characteristic features of the machine proposed to him. It can be assumed that 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 complaints about the Steam Wheel Tank concerned insufficient mobility and maneuverability, which was demonstrated already during the first test drive to the landfill. Having developed the required steam pressure, the existing power plant showed acceptable characteristics, however, the specific power was not more than 9 hp. per ton imposed certain restrictions on the general characteristics of mobility. The second factor that had a negative impact on the mobility of the tank was the wheeled chassis. Despite using the widest wheels, the pressure on the supporting surface was too great and provoked burrowing on soft soils.
Steam engine diagram
The proposed set of small arms and cannon weapons, on the whole, looked satisfactory. At the same time, the limited aiming angles of guns and machine guns, as well as the distribution of weapons in different sectors, could be considered disadvantages. Also, the fighting qualities were negatively affected by the impossibility of transferring fire to a large angle without turning the entire machine, which was made difficult by the use of an imperfect steering system with a rotary roller.
However, it must be admitted that the designers of Holt, who previously developed the 150-ton "Field Monitor", took into account their mistakes, and therefore the new project of the Steam Wheel Tank was more successful. First of all, the authors of the new project abandoned the idea of increasing the size and using 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 the prototype.
Nevertheless, the new project of the steam tank was based on not the most successful ideas, which led to a natural sad ending. During short tests, the only prototype built could not show high performance, and therefore did not go into production, and later went for disassembly. Empirically, another scheme of an armored combat vehicle was revealed, which should not have been used when creating new military equipment.
