What Made the Chrysler A57 Multibank the Strangest Engine of World War II?
The Pentar symbol of Chrysler is one of the most powerful and recognizable logos in the history of the automotive industry.
But behind those five star points lies a mechanical secret that not everyone knows.
Imagine a machine built by combining components that seemed impossible to unite.
Forming a strange structure designed to power Sherman tanks across brutal battlefields.
Why did Chrysler choose a solution so complex, so extreme instead of following more conventional paths?
And could this one-of-a-kind design truly be the hidden soul behind the legendary Pentar emblem?
Today we will unravel the story of the Chrysler Multibank, an engineering marvel that helped Chrysler assert its position as a true engineers empire.
In 1941, as the war spread and time became the greatest enemy, Chrysler did not have a true tank engine at its disposal.
Instead of starting from a blank drawing board, they chose a pragmatic path using what was already available.
Five flathead inline 6 engines with a displacement of 251 cub in units already being mass- prodduced for civilian vehicles were brought together into a single assembly.
Not to operate independently, but to work collectively to generate the pulling force required for a war machine weighing dozens of tons.
The A57 multi-bank structure resembled no tank engine that had come before it.
Five six-cylinder banks were arranged in a star-like pattern around a central shaft.
Each bank retained its own crankshaft, but all torque was gathered through a complex gear system.
Five satellite gears meshing with a single central gear.
This central gear was the true heart of the system.
It not only collected power, but also drove the cooling fan, the fan clutch, and transmitted power directly to the tank’s gearbox.
Here, Chrysler needed a system that could be assembled quickly, repaired in the field, and survive damage.
The central gear design allowed exactly that.
If one bank encountered trouble, the remaining banks could continue turning.
In practice, this configuration was deployed on a large scale.
More than 100 Lee tanks and nearly 7,500 Sherman tanks were equipped with the A57 multibank.
These vehicles were not fast, but they were durable, climbed well, and most importantly, they could keep moving under harsh conditions.
The A57 was not born to race.
It was born to endure.
Placing the A57 alongside its contemporary rival reveals a clear difference in philosophy.
Ford Motor Company developed the GAAV8, a 60° V8 with a displacement of roughly 1,100 cub in dual overhead cam shafts and a flat plane crankshaft.
Ford chose a unified engineering approach.
Fewer components, more compact, easier to control.
The A57, by contrast, was a labyrinth of gears and rotating shafts.
And the A57 Multibank was not free from teething problems in its earliest production runs.
On paper, the idea of combining five commercial engines made sense.
But once exposed to battlefield reality, individual subsystems began to reveal weaknesses.
Most notably, the cooling system.
Initially, each six-cylinder bank was equipped with its own water pump driven by a belt.
The problem was that the load across the banks was never perfectly balanced.
Some belts worked harder, ran hotter, and failed sooner than expected.
When a belt failed, temperatures rose rapidly, triggering the risk of cascading failures.
For a tank, this was unacceptable.
Chrysler’s solution was not to patch the problem, but to restructure the system.
The entire setup was converted to a single water pump driven directly from the accessory shaft connected to the central gear.
This ensured consistent coolant flow to all five banks while completely eliminating reliance on belts.
In return, the radiator had to be redesigned with a shaft passing straight through the cooling core, a highly unusual feature rarely seen on either tank engines or civilian power plants.
But it worked.
And in wartime, that was the only criterion that mattered.
The fuel and ignition systems also clearly reflected the philosophy of keep what already works.
Chrysler never combined the distributors.
Throughout the F57’s entire service life, five distributors remained, one for each bank.
This made battlefield diagnostics easier.
When something failed, technicians could isolate and address it directly.
The carbburation system, however, was significantly improved.
Instead of being scattered along the sides of each cylinder bank, the carburetors were relocated to the top of the engine.
This new layout simplified throttle linkages, reduced synchronization errors, and more importantly made maintenance feasible within the cramped confines of a tank engine bay.
The lubrication system provided another example of practical evolution.
The original design with multiple oil pumps proved unnecessary and overly complex.
Eventually, Chrysler adopted a two pump configuration.
One scavenge pump returning oil to the reservoir and one high-pressure pump delivering oil to all five cylinder banks.
This approach ensured stable oil pressure, reduced the risk of localized oil starvation, and cut down the number of failureprone components.
When looking at the specification sheet, the Chrysler A57 multibank does not impress in the familiar way of high-performance engines.
Every number associated with the A57 reflects a very clear philosophy, prioritizing torque, durability, and the ability to operate continuously under heavy load.
The A57 is a textbook under square engine.
The piston bore measures just 3.44 in, while the stroke extends to 4.5 in.
This configuration limits high revving capability, but in return delivers strong pulling force from low engine speeds.
For a tank weighing more than 30 tons, that matters far more than any horsepower figure on paper.
The engine does not need to accelerate quickly.
It needs to pull, push, and sustain movement through mud, sand, and terrain torn apart by artillery.
Its total displacement of 1,253 cub in equivalent to more than 20 L is distributed across 30 small cylinders.
Peak output ranges from roughly 370 to 445 horsepower depending on version and tuning.
That may sound modest given the enormous displacement, but that is a sports car way of reading specifications.
With the A57, the real story lies in the torque curve.
Broad, flat, and ready to work at low RPM for extended periods.
This is what allowed Sherman tanks to climb hills, overcome obstacles, and keep moving even when conditions were far from ideal.
Another valuable technical detail is the use of sodium filled exhaust valves.
At high temperatures, the sodium liquefies and transfers heat from the valve head to the stem, improving heat dissipation.
In a 30cylinder engine where heat buildup is a constant enemy, this solution significantly enhanced durability.
It is not glamorous, but it demonstrates how clearly Chrysler understood the limits of its materials.
In operation, the A57 was not smooth by civilian standards, but it was stable in a distinctly military way.
The dense firing rhythm of 30 cylinders produced a low, steady sound with almost no pauses.
It was a sound crews learned to trust because when it went silent, the problem was usually serious.
More importantly, after the initial improvements, the A57’s reliability reached a level comparable to single block tank engines such as the 4G AAV8.
Complexity was no longer a fatal weakness, but rather the price paid for a solution that maximized available resources.
Looking back at the Chrysler of 57 multibank from a historical distance, it is easy to label it an overly complex design, but that is a peaceime judgment.
In the context of World War II, when every month of delay cost lives, the A57 was a solution that was coldly rational.
After its early issues were resolved, its realworld reliability was recorded as comparable to single block tank engines like the Ford GAV8.
The difference lay in the path taken to reach that result.
The greatest value of the A57 was not in its specifications, but in its ability to leverage an existing ecosystem.
Chrysler transformed commercial automotive engines already familiar to mechanics into a unified military power plant.
After refinement, maintenance was no longer the nightmare many imagined.
A failure in one bank did not mean the entire engine stopped.
In many cases, the vehicle could still withdraw from the front lines under its own power for repairs.
That was a genuine tactical advantage, one that never appeared in brochures or comparison charts.
From a purely technical standpoint, the A57 left no direct lineage.
No one continued to develop multibank engines of this type for tanks or civilian vehicles.
But its influence did not need to follow a direct path.
The A57 proved that Chrysler possessed extraordinary production flexibility and was willing to accept technical risk to meet strategic demands.
That mindset became the foundation for later achievements from HMI engines to postwar racing programs.
And then there is the symbolic question.
Could the structure of five cylinder banks arranged around a central shaft have inspired the Pentar logo?
There is no official documentation confirming this, but visually and spiritually the resemblance is difficult to dismiss.
A five-pointed star born from machinery, from war, from the need to unite separate components into a single hole.
The Chrysler, a 57 multibank, was not the pinnacle of simplicity, nor was it an engine designed to endure forever, but it stands as clear proof of Chrysler’s engineering capability at its most difficult moment.
A machine created not to impress but to fulfill a mission.
And in the history of mechanical engineering that is sometimes the most enduring legacy of all.
Today the A57 multibank no longer has a direct influence on modern engine design.
But its story still holds its full value.
It is a lesson in adaptation in engineering that serves a purpose greater than itself.
