First News of the American
Page 21
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Mark IV Tank
I N the construction of American- Tanks, the automobile industry is playing a big part. As is generally_ known, the M3 or General Grant type has been produced by the Chrysler Corporation, which put down a special plant for its 'manufacture long before America came into the war. Although mounting a 75-mm. gun as its main armament, this suffers from limited traverse as it is mounted on the side of the Tank and hence can be freely fired only to starboard, it being necessary to turn the whole Tank round to coVer a good field of fire on the opposite side. Further, the M3 Tank is powered by a 450 h.p. radial air-cooled engine, and
although it has stood up to the work well it does not have high torque at low speeds—a valuable feature—nor a particularly long life between overhauls. Hence, the M3 has been followed by a modified edition called the M4, which is described in some detail in one of thd latest issues of " Auto= motive Industries."
The M4 has been built by the Fisher Body Division of General Motors and
is of an all-welded construction, scaling 30 tons (2 tons more than the M3). It mounts thesame type of 75 mm. gun, but in a top turret which gives unlimited traverse through 360 -degrees.
Thcparts for the frames are held in fixtures, being so designed that the parts can be revolved in a complete circle, elevated or lowered as needed. It is thus possible to do all the welding with the operator leaning forwards, making for a faster and better wel8 than if the man had to work underneath the job and reach upwards. The first Fisher-built Tank has already undergone extensive tests and received favourable reports.
The radial engine, which suffers from the disadvantage of increasing the height of the Tank, has been discarded in favour of a two-bank, twostroke General Motors oil engine having 12 cylinders and developing 450 h.p. This engine has a much greater cruising radius on a given tank of fuel and will run 15 times longer between overhauls, than the adapted aero engine. It will be seen from an illustration that the engine is virtually two siNrcylindered units tied together,' being supercharged by a Roots-type blower.
" Automotive Industries " reports that the Ford concern also intends to produce the M4 type of Tank, but it is planned to use a V$ conversion of Ford's 12-cylinderecl liquid-cooled aero engine. It is expected that this unit will develop more than 500 b.h.p.
Chrysler, says "Automotive Industries," will also abandon the M3 in the course Of the next few months and build the M4. This organization has been experimenting with a power plant consisting of five 125 b.h.p. car-type engines grouped around a central crankshaft.