American cooperation with Britain was even closer than with the French, resulting in the Mark VIII International heavy tank: a tank that was designed in Britain, equipped with an American engine, and built in the United States. Of course, analogous tanks were also designed in the US, but it was the designs with foreign roots that became the catalyst for the development of American heavyweight tanks.
The situation with medium tanks developed in a similar fashion. While there were more or less successful attempts to create light and heavy tanks during WWI, the medium class was practically absent. An attempt to create a medium tank named "Tracklayer Best 75" was a design based on the Holt 75 tractor. While this tractor served as a base for tracked vehicles in Britain, Germany, and France, the American attempt failed. A prototype was built in 1917, but it was only suitable for propaganda purposes, which it excelled at.
However, the American military needed a tank for more than just propaganda. The ordnance bureau looked across the ocean for inspiration. The Americans were in no rush, as the contemporary British tanks of the time were far from ideal. The Medium Tank Mk.A Whippet was rapidly becoming obsolete, and its successors, the Medium Tanks Mk.B and Mk.C, seemed like a step back.
A suspension patent by Philip Johnson. Some of its elements look far from normal.
It's worth mentioning that during WWI, medium tanks played second fiddle, with the exception of the Schneider CA1. It became not only the first French mass produced tank, but the first combination of relatively low weight, decent armour for its time, and powerful armament, including a short 75 mm gun. The British only equipped their medium tanks with machineguns, which limited their effectiveness. However, the French tank was not without vital flaws.
William Tritton was the main designer of British tanks at the time. Close to the end of the war, he gained a worthy opponent: Major Philip Henry Johnson. He was the unofficial head of the central tank workshops in France and knew all too well about the drawbacks of Tritton's designs. According to Johnson, medium tanks needed agility that Tritton's designs could not achieve; the suspension of Britain's first tanks did not allow them to accelerate past 12 kph.
Johnson's first experiments, already in the rank of Lieutenant Colonel, consisted of installing a new sprung suspension on the Whippet. It was obvious that this was just half-measure. A new tank had to be built from scratch, and that is what Johnson did.
According to his theory, a medium tank had to reach a speed of 20 mph (32 kph). Taking the Whippet as an inspiration, he designed a tank that was radically different from Tritton's designs. The 13.5 ton tank had a Wolseley Puma 240 hp engine, which gave it an impressive power of 17.7 hp/ton.
This was just the beginning. Johnson designed a new suspension that had nothing in common with the British "rhombus". It was both revolutionary and strange: the spring element consisted of a steel cable stretched along the side. If the cable snapped, all bogeys along one side lost their springs. Servicing a suspension like this was torture. Nevertheless, the design functioned well.
The same can be said about Philip Johnson's track link. One feature was that it could tilt sideways, giving better ground grip on complicated terrain. Each track link had a wooden pad, which improved driving on roads.
Medium Tank Mk.D Modified, Johnson's final tank. Note the cupola behind the casemate: this is where the driver sat.
Johnson's tank was indexed Medium Tank Mk.D. Several prototypes were built in 1919. They were phenomenally fast for their time, but trials revealed many issues. The Medium Tank Mk.D never became anything more than an experimental design, but that didn't stop it from achieving its place in history. It was not only the first tank to go faster than 30 kph, but the first amphibious tank in the world. It didn't swim fantastically well, but that was already an achievement.
The French became interested in the novelty and tested a similar suspension on the Char B, but the Americans went even further, interested in the tank as a whole.
Engine Famine
The issue of purchasing one of Johnson's tanks came up in June of 1919. Major R.E. Calson, a member of the British-American tank commission, played a significant role in the decision to use the Mk.D concept. The goal was not to copy the British tank, but to create a new one that was similar to the British design.
This was connected to the fact that the Medium Tank Mk.D required very serious modifications to the way that it was built. It's enough to say that Johnson put the driver in the rear of the fighting compartment, giving him poor visibility. The armament, consisting of three machineguns, was also unsatisfactory. Neither was their placement in an immobile casemate; experience in WWI dictated that a tank needs to have a rotating turret.
Full sized model of the Medium A Tank, April 1920
On August 18th, 1919, the requirements for the medium tank were approved by Brigadier General Samuel D. Rockenbach, the new commander of the tank corps. Rockenbach was with the tank corps from the beginning and had significant experience in combat. He understood what kind of tank his subordinates needed.
According to initial specifications, the tank would weigh 18 tons and have an engine that gave it at least 10 hp/ton. The top speed of the tank would be 19-20 kph, and carry enough fuel to travel 100 km. The tank would be armed with one cannon and two machineguns. The armour would protect the tank from rifle caliber bullets at all ranges. However, this requirement was revised on November 4th, 1919. The tank now had to be protected from 12.7 mm bullets.
The gun could be aimed vertically and horizontally.
A new organization began the development of the tank: the technical department of the tank corps in the Rock Island Arsenal. The full sized model was ready on April 2nd, 1920. The resulting tank differed significantly from the Mk.D design, and was far from just a copy. The new tank was an independent and very progressive design. Almost nothing was left from its British ancestor aside from the concept of a tank with a long hull, front fighting compartment, and rear engine/transmission compartment.
A decision was made to build two experimental tanks on April 13th, 1920. The first was built with an American suspension, the second with a suspension from the original Medium Tank Mk.D. Priority was given to the domestic design. The first prototype was indexed Medium Tank M1921, and its assembly was finished in December of 1921.
Medium Tank M1921 at the Aberdeen Proving Grounds, February 1922. The tank still carried its old index.
Overall, the design was the same as the model presented in April of 1920. Due to the changes in requirements, the mass of the tank increased to 18.5 tons. The armour was 25 mm thick, making the Medium Tank M1921 the first tank in the world to be reliably protected from high caliber machineguns.
The armour wasn't the only progressive element. Unlike its British ancestor, the M1921 carried its armament in two turrets. The main turret had a 6-pdr (57 mm) gun and a 7.62 mm Browning M1919 machinegun. The gun mount allowed it to be traversed horizontally or vertically with a shoulder stock. This decision, copied from the Renault FT, was used on many American tanks up to 1942.
The second turret (an overgrown commander's cupola) was installed in the roof of the main turret, and another M1919 machinegun was installed in it. The driver was placed in the driver's compartment, in the front of the hull. In total, the tank was crewed by 4 men working in rather comfortable conditions.
The suspension of the Medium Tank M1921 differed radically from the one used on the Medium Tank Mk.D. It was designed by an engineer named Emil Francis Norelius, who worked for the Holt company. Back during WWI, Norelius designed several SPGs on tractor chassis. Since all of those designs were built under the Holt brand, the talented engineer's name was left in obscurity. His input in the suspension of the Medium Tank M1921 also remained unknown to most.
Instead of the complicated system with cables, Norelius proposed the use of more traditional suspension elements that he developed for Holt. The tank's tractor past is given away by the drive sprocket and idlers, as well as the track links. This suspension was suitable for a tank that was not expected to drive faster than 20 kph. Removable armour screens protected the suspension from enemy fire.
Murray and Tregurtha engine which practically killed the Medium Tank M1921.
The Achilles' heel of the Medium Tank M1921 was the engine. The American military chose Murray and Tregurtha Inc, specializing in shipbuilding and naval engines, as a subcontractor. The company decided to not reinvent the wheel and adapted a naval V-shaped engine for the tank. Nominally, the engine output 220 hp, but in practice it never achieved more than 195 hp. The result was that the tank could barely drive faster than 16 kph at trials at Aberdeen, which began in February of 1922. The engine was also unreliable, which caused additional problems.
Attempts to resolve the situation with the engine lasted for four years. The fastest solution was the use of a more powerful engine. This engine was found quickly: the Liberty L-12 aircraft engine used in the Mk.VIII International. The 338 hp engine doubled the tank's maximum speed, but at the cost of constant breakdowns. Miracles don't happen: the transmission and suspension were not designed for this kind of power and speed, and the results were predictable.
Medium Tank M1922 with a Medium Tank Mk.D type suspension.
The second tank, indexed Medium Tank M1921, arrived at the Aberdeen proving grounds on March 1st, 1923. The armament, hull, engine, and other components were the same as on the Medium Tank M1921. The only difference was the suspension. Engineers from the technical department copied the suspension from the Medium Tank Mk.D, but with some changes. The suspension with a cable and tilting track links with wooden pads remained.
The trials gave complicated results. On one hand, Philip Johnson's suspension allowed the tank to reach a speed of 26 kph, which was more than what was required. On the other hand, the expected issues with such a complex suspension made themselves known. The steel cable snapped multiple times. It was eventually replaced with a chain, which improved the suspension's reliability. However, the engine issues remained. Despite the superior mobility, Johnson's suspension was rejected. Servicing a suspension like that could turn the crews' lives into hell.
Philip Johnson's suspension couldn't be any simpler! Now imagine that the cable snaps...
Conditionally Approved
Despite problems with the engine, the Ordnance Bureau did not lose hope of getting the tank to an acceptable condition. As a result of experiments, it was decided to focus on the Medium Tank M1921. In 1925, the American military signed a contract with the Packard Motor Company to develop a special tank engine. In June, the 8 cylinder V-shaped engine was installed into the Medium Tank M1921. Trials showed that the new engine was superior to the old one.
Various changes made in 1925 and 1926 raised the tank's mass to 23 tons. However, new elements of the drivetrain increased its reliability, and the speed remained at acceptable levels.
Joint patent for the Medium Tank M1921 design. Levin H. Campbell Jr. was Norelius' co-author, another key figure in the American armed forces in the WWI years.
This success was cause for further improvement of the Medium Tank M1921 design. A decision was made to build a third tank, indexed Medium Tank T1. Since the military's budget was cut severely after the end of the war, the Ordnance Committee decided to forego using armoured plates on their experimental vehicle. Instead, the tank was made from mild steel, which reduced the cost tenfold (from $52,000 to $5,200). Since the tank was expected to be a test subject, the decision was well founded.
Medium tank T1, Aberdeen Proving Grounds, July 1927
The tank built in May of 1927 was overall a repeat of the M1921. The suspension was the same as its predecessor, aside from new "skeleton" tracks designed by Harry Knox. These track links were more suitable for high speeds. The turret design was almost unchanged. The hull was slightly altered, mostly the engine compartment.
The mass of the tank was 19.9 tons, and the 200 hp Packard engine gave it more than the 10 hp/ton that the military wanted. The tank achieved a speed of 18 kph in trials that started in July of 1927, and once even hit 22.5 kph. According to the American military, this was not enough. On the other hand, the tank was very reliable. It was not surprising that, after the trials ended, the Ordnance Committee insisted on standardizing the tank. On February 2nd, 1928, it was accepted into service under the index Medium Tank M1.
Medium Tank M1 and its crew, spring of 1928.
One would expect that 6 years of trial and error would have given the Americans a fully fledged medium tank. The problem was that this was the late 1920s, and the Medium Tank Mk.D concept was obsolete by then. Even worse, the ordnance department launched a program to develop a new 15 ton medium tank in 1925. The success of another one of Knox's designs, the Light Tank T1E1, inspired the idea of building an enlarged version. From the fall of 1926 onwards, Harry Knox led the development of this medium tank, initially indexed Medium Tank M1924.
In the spring of 1928, the standardization of the Medium Tank M1 was cancelled, and it reverted to being called Medium Tank T1. John Walter Christie poured oil on that fire, unexpectedly entering the competition with his M.1928. In 1931, three tanks were competing for the title of the American medium tank instead of one. By then, the Medium Tank T1 fell far behind.
75 mm M1920 howitzer in a Medium Tank T1 turret.
Despite this turn of events, work on the Medium Tank T1 did not end. For starters, a 75 mm M1920 howitzer was installed. This significantly improved the firepower of the tank. Trials against a light M1917 showed that a hit from a howitzer shell broke its armoured plates into pieces. Despite such an impressive effect, the tank's original gun was returned. A second attempt to install the Liberty L-12 engine was made in April of 1932. The modernized tank became known as the Medium Tank T1E1.
The tank was sent to Fort Benning, the main location of American infantry tanks. The tank was included into the 2nd Tank Company, which was reformed into the 67th Infantry Company in October of 1932. Fort Benning became the battlefield for the three competitors: the Medium Tank T1E1, Medium Tank T2, and Christie Convertible Medium Tank T3.
Medium Tank T1E1 in the 67th Infantry Company armed with medium tanks. The tank received a personal name, "Fu Manchu", after a fictional villain.
On one hand, the Medium Tank T1E1 inherited all of the problems of the Medium Tank M1921 along with its engine. The tank was pursued by constant breakdowns of the chassis and drivetrain. On the other hand, its speed grew to 40 kph.
The mobility of the lighter Medium Tank T2 turned out to be no better than its competitor. The practical top speed was 32 kph. The suspension, also a descendant of a tractor, did not allow it to go any faster. The armament was also not particularly better. The 47 and 37 mm guns had only slightly better penetration than the 6-pdr. At the same time, the fighting compartment of the Medium Tank T1E1 was much roomier, and there was potential to install a more powerful gun.
Trials quickly showed that both tank designed by the Ordnance Department were inferior to Christie's tank, which was significantly faster and more reliable. Its armour and armament was not as good as its competitors', but high maneuverability was one of the most important factors for the American military. The 37 mm infantry gun and coaxial machinegun were enough for infantry support.
As a result, most of American medium tank development in the 1930s concerned convertible drive vehicles. The Medium Tanks T3E2 and T4 continued Christie's designs, while the Medium Tanks T1 and T2 were left in the junkyard of history.
The Medium Tank M1922 led a harsh life, but avoided the scrap yard.
The Medium Tank M1921 and Medium Tank T1E1 were scrapped. As for the Medium Tank M1922, it was spared. The tank was left in the Aberdeen tank museum, escaped the massive write-off of exhibits in 1952, and survived more than half a century worth of exposure to the elements. Currently, the tank can be found in Anniston, Alabama, after Aberdeen's tank museum was moved to Fort Lee. Currently, the tank is awaiting a decision on its final destination.
No comments:
Post a Comment