In order to successfully complete the assigned task and not fall under the enemy's retaliation, an artillery gun must have high mobility. The obvious solution to this problem is to mount the gun on a self-propelled chassis, but such a combat vehicle is complex and expensive. A simpler and cheaper option for increasing mobility is to create a self-propelled weapon. In the early sixties, the XM124 self-propelled howitzer entered the test range in the United States.
By the early sixties, the American command managed to learn about Soviet projects in the field of self-propelled guns (SDO). Such weapons, capable of moving around the battlefield without a tractor and the help of a crew, were intended for airborne units and seriously increased their combat potential. Albeit with the most serious delay, the US Army became interested in this concept, resulting in an order for the development of two new projects. Upon successful completion, they could change the appearance of army artillery.
It should be noted that the US military did not want to directly copy foreign decisions. Soviet SDOs were mobile anti-tank guns, and the US command considered it necessary to develop self-propelled howitzers. At the same time, the development of two LMSs with different calibers was ordered. The purpose of the first project was to refine the serial 155 mm M114 howitzer, and the second was to be a mobile modification of the M101A1 105 mm howitzer.
Howitzer M101A1 in original configuration
Projects of a similar kind have received appropriate designations. The more powerful self-propelled gun was named XM123, and the smaller caliber system was named XM124. In both cases, the working titles of the projects included the letter "X" indicating the status of the item, and in addition, did not reflect the type of the base sample in any way. Subsequently, new letters were added to the original designations, with the help of which the next modifications were highlighted.
The development of the LMS of the XM124 type was to be carried out by two organizations. The overall project management was carried out by the Rock Island Arsenal Design Department. He was also responsible for the artillery unit and gun carriage. All new units were to be created and supplied by the commercial company Sundstrand Aviation Corporation. At the same time, American Machine and Foundry was working with the Rock Island Arsenal to develop the XM123 howitzer. For obvious reasons, the creation of both howitzers was not trusted by one developer, and two private companies were involved in the SDO development program at once.
The two new models were created by different companies, but had to be built according to general principles. According to the terms of reference, the designers had to preserve the maximum possible number of parts of the existing gun and gun carriage. It was necessary to create a set of components suitable for installation on a howitzer without significant alteration. Also, the requirements specified the approximate composition of the new units and their principles of operation. It should be noted that the first versions of the two LMS did not suit the customer, as a result of which the projects were redesigned. The modernization of the two howitzers was also carried out using common ideas.
All the main units of the existing weapon were transferred to the XM124 project without major changes. So, the artillery unit was used in its original form, and the existing carriage with sliding frames was now equipped with new devices. The wheel drive, which has become the drive axle, has been significantly redesigned with the introduction of new devices - including engines. According to the results of this revision, the howitzer did not change its fire characteristics, but received mobility.
The M101A1 towed howitzer and its self-propelled modification were equipped with a 105 mm rifled barrel. The barrel length was 22 caliber. The barrel was not equipped with a muzzle brake. In the breech there was a chamber for a unitary shot and a semi-automatic horizontal wedge bolt. The barrel was mounted on hydropneumatic recoil devices. The brake and knurler were located under the barrel and above it. As part of the swinging part, a cradle with an elongated rear rail was used, which was necessary due to the length of the rollback 42 inches (just over 1 m). A manual vertical aiming drive was fixed on the cradle.
The gun carriage was distinguished by its comparative simplicity. His upper machine was small in size and was a U-shaped device with attachments for the swinging part and for installation on the lower machine. It also had two side sectors for vertical guidance and one for horizontal.
The lower machine was built on the basis of a crossbeam with attachments for all necessary units, including beds and wheel travel. When creating the LMS XM124, the design of the lower machine has undergone some minor changes. First of all, the engineers had to consider the possibility of installing new motors and gearboxes to drive the wheels. All new devices were mounted on the existing beam.
The gun was equipped with a pair of sliding beds of sufficient length and strength. Devices of a welded structure were hingedly mounted on the lower machine. To keep the tool in position in the rear of the bed, openers were provided. As in the XM123 project, one of the beds was supposed to become the basis for the installation of new units.
The M101A1 howitzer and its self-propelled version received a composite type shield. On the sides of the swinging part, two flaps of similar shapes and sizes were fixed on the upper machine. Two more protection elements were installed on the lower machine, directly above the wheels. They consisted of two parts: the top could be folded, improving visibility. Another rectangular flap was located under the lower machine. In the combat position, it went down and blocked the ground clearance, in the stowed position - it was fixed horizontally, without interfering with the carriage.
The gun was equipped with sighting devices that provided direct fire and from closed positions. With the help of manual drives, the gunner could move the barrel within a horizontal sector with a width of 46 ° and change the elevation from -5 ° to + 66 °.
XM124 at the test site during sea trials
In the first version of the XM124 project, almost the same power plant was used as on the XM123 SDO. A tubular frame was placed on the left frame of the gun, on which all the necessary devices and the driver's workplace were located. In addition, some of the new devices appeared on the front of the lower machine - next to the wheel drive.
A pair of air-cooled gasoline engines with a capacity of 20 hp was placed on the frame. each. It is possible that the engines of the Consolidated Diesel Corporation were used, similar to those used in the 155-mm SDO project. In front of the engines were a pair of hydraulic pumps that created pressure in the lines and were responsible for transferring energy to the wheels. The first versions of the XM123 and XM124 projects used a hydraulic transmission of a fairly simple design. The liquid was piped to a pair of hydraulic motors mounted on a gun carriage. They rotated the wheels through compact gearboxes. In fact, the gun had two separate hydraulic systems, one for each wheel. The wheels retained hand-operated parking brakes.
The driver's seat was mounted directly on the pump. On the sides of it were two control levers. Each of them was responsible for supplying fluid to their own hydraulic motor. Their synchronous movement made it possible to move forward or backward, and differentiated provided maneuvering. From the point of view of controls, the XM124 LMS was a little more convenient than the XM123, where all control was carried out by a single lever swinging in two planes.
Directly under the power unit on the bed, in front of the opener, a small diameter caster was placed. When driving, it had to take on the weight of the beds and new units. The wheel rack had swivel mounts, which made it possible to fold it when deployed into position.
After the modernization, the overall dimensions of the gun remained the same. The length in the stowed position did not exceed 6 m, the width was 2, 2 m. The total height was slightly more than 1, 7 m. In the basic version, the howitzer weighed 2, 26 tons; the new modification XM124 was noticeably heavier due to the special configuration. At the same time, the firing qualities should not have changed. A 22-caliber barrel accelerated projectiles to speeds of the order of 470 m / s and provided firing at a range of up to 11.3 km.
In the stowed position, the XM124 self-propelled howitzer rested on three wheels, two of which were leading. Riding was carried out with the barrel forward, while the gun and carriage limited visibility from the driver's seat. Upon arrival at the firing position, the calculation had to turn off the engines, apply the brakes of the main wheels, and then raise the bed and fold the rear wheel to the side. Further, the beds were spread apart, the openers were buried in the ground, and the howitzer could fire. The transfer to the stowed position was carried out in the reverse order.
Its own power plant was intended to move between closely spaced firing positions. For transportation over long distances, the XM124 needed a tractor. In this case, it was necessary to raise the rear wheel, which could interfere with normal transportation.
In mid-1962, the Rock Island Arsenal and the Sundstrand Aviation Corporation brought the first prototype of a promising weapon to the test site. In parallel, the 155-mm XM123 howitzer was tested on the same site. The 105 mm caliber system showed not too high, but acceptable mobility characteristics. As expected, its own speed was lower than when transported by a tractor. On the other hand, rolling the howitzer by hand was even slower. However, the power plant and transmission needed improvement.
Fire tests of two LMS ended with similar results. In the firing position, the weight of the engines and the hydraulic pump fell on the left frame, which upset the balance of the gun. When fired, the howitzer was blown back and simultaneously turned in a horizontal plane. This fact seriously hampered the restoration of the aiming after a shot and sharply reduced the practical rate of fire.
After testing, both guns were sent for revision. Based on the results of the new design stage, the XM124E1 and XM123A1 SDOs were brought to the landfill. In both cases, the most serious modifications were made to the new units responsible for the movement. One of the engines was removed from the bed of the 105-mm howitzer, as well as both pumps. Instead, they installed an electric generator and new traffic controls. The hydraulic motors on the lower carriage were replaced with electric motors.
The only surviving sample of the LMS XM124, allegedly related to the "E2" modification
The new version of the gun was tested and showed its potential. The electric transmission did not differ much from the hydraulic one in terms of its efficiency, although the new power plant had noticeably less weight. Otherwise, the two modifications of the CAO were similar. At the same time, the abandonment of the engine and pumps did not allow getting rid of the problem with turning when firing. The left frame still outweighed and caused unwanted movements.
There is information about the development of the XM124E2 modification, but it raises serious questions and doubts. A weapon of this type is on display at the Rock Island Arsenal Museum. The information plate indicates that the presented product belongs to the "E2" modification and is the third experimental gun in the series. At the same time, in any other sources, the XM124E2 SDO is mentioned only in the context of a museum exhibition. In addition, the museum piece is equipped with a hydraulic transmission, which raises new questions.
It is quite possible that on the site of the museum there is a self-propelled howitzer XM124 of the very first modification, assembled according to the original project. As for the information plate, it may be erroneous. However, it cannot be ruled out that the third modification of the LMS was nevertheless developed and had the maximum resemblance to the basic one, but for some reason full information about it did not become public.
According to various sources, in the early sixties, the Rock Island Arsenal and the Sundstrand Aviation Corporation built and tested up to three prototypes of two or three types. Serial howitzers, equipped with new devices, could independently move around the battlefield, but their mobility still left much to be desired. In addition, they were improperly balanced, resulting in unacceptable displacement when fired. In this form, the XM124 and XM124E1 SDOs were not of interest to the army. By the middle of the decade, the customer ordered the termination of work on unpromising projects.
One of the experienced XM124s later ended up in the Rock Island Arsenal Museum. The fate of the others is unknown, but they could have been returned to their original state or simply taken apart. The only known example of such weapons is now a mystery and leads to some confusion.
The projects of the self-propelled guns XM123 and XM124 were based on common ideas and used similar units. As a result, the real characteristics and capabilities, as well as the disadvantages and problems, turned out to be the same. Both howitzers did not suit the army, as a result of which they were abandoned. In addition, due to the failure of the first projects, work on the entire topic of self-propelled guns was stopped for several years. A new sample of this kind appeared only at the beginning of the seventies.
