The M1 Abrams is regarded by many as the best main battle tank in the world. While several countries
certainly have some excellent contenders for first place, the Abrams’ has a secret weapon that gives
it the edge over its competition. Hidden deep inside the belly of the tank is what gives it
the ability to shoot and move like it does: the Honeywell AGT 1500 gas turbine engine. Let’s
take a closer look at why this engine is so OP. For starters, the engine is an absolute beast.
Utilizing a gas turbine engine with both high and low-pressure compressors combined with a
high and low-pressure power turbine, it produces a mind-boggling 1500 horsepower of energy. When
put into the tank, this can propel the Abrams an impressive 45 mph on roads and about 30 mph
off-roads. With the Abrams being one of only two tanks in service with a gas turbine engine, the
other being an early version of Russia's T-80, the story of how it came to be might be surprising.
If you were thinking why the Abrams has a literal jet engine, you wouldn’t be the only one raising
an eyebrow. During its development, it was also a controversial subject. In the early 1960s,
the US decided they wanted to increase the lethality of their main battle tank. While
the M60 had served well, many people considered it a very underpowered tank. Weighing in at over
50 tons combat loaded, it was one of the heaviest tanks the US had fielded to this
point and was the heaviest main battle tank in service. But there was just one problem.
Powering the M60 was a Continental diesel engine that produced just a measly 750 horsepower,
and this severely limited both on-road and off-road speed and maneuverability. With
the Soviets developing faster tanks, American army officers did not want their tanks to be
outrun and outflanked by Soviet tank formations simply because they could not move well. They
also knew that American tanks would continue getting heavier with increased armor to defeat
developing Soviet guns and ammunition. Because of this fear, the military began a joint effort
with the West Germans in their MBT-70 project. The MBT-70 was supposed to use the expertise
in German engineering to build a better tank engine for the project. After all,
Defense Secretary Robert McNamara was apparently a huge fan of German engineering and believed
that the two nations could build an unstoppable tank with their engines and American guns and
armor. However, not all went according to plan. German tank development had not kept pace with
Cold War developments. Differences in opinion and soaring costs started making Congress officials
doubt the project. With costs ballooning several times above initial estimates, Congress pulled the
plug. While the DoD was directed to develop a new tank, they would have to do so cost-effectively.
With their marching orders in hand, Army officials began their next project, the XM803,
which later morphed into the XM-1 project. Over the next decade, the Army experimented
with numerous radical design changes meant to increase the lethality of American tanks,
not just now but for generations to come. One of those revolutionary changes was picking a gas
turbine engine over traditional diesel or gasoline engines, a decision spurred by the engine’s
effectiveness in helicopters during the 1960s. Lycoming was the first company to produce aircraft
engines for the Army. Its state-of-the-art design was lighter and more powerful than
traditional engines. This was a big deal as it allowed helicopters to carry more fuel, ammo,
or people. The gas turbine engine family they developed was also less maintenance intensive
than previous helicopter engines. Though the initial cost was higher up front, over time,
the cost per flight hour went down as aircraft spent less time on the ground getting serviced.
With this idea in their mind, Army officers decided to do the same thing for tanks. After all,
the cost proposals from the two main competitors were not too far off from one another. However,
the increased cost savings from less maintenance enticed Army leadership to take the plunge since
maintenance costs make up the bulk of a tank's price tag for most of its life.
After awarding the contract to Chrysler, which eventually became General Dynamics Land Division
after Chrysler sold its stake in its military production plant, the engine started being
tested. Results among the troops who first used the vehicles were more than stellar.
While things like gunnery and armor were, of course, high on the list, its ability to move
quickly surprised all the stakeholders, but there was just one problem. The tank,
as predicted, was a gas guzzler. Even though this didn’t shock anyone, the main problem was
that initial models were not equipped with an Auxiliary Power Unit that forced tankers
to run the engine on idle and burn through fuel. In the tank world, an Auxiliary Power Unit is like
a mini-engine. Its purpose is to provide power to the tank's main systems like its fire control,
night vision, and fire suppression systems. Before the introduction of APUs, tank crews
of old had to run their vehicles' engines all the time, wasting fuel and making the tank easier to
spot. By incorporating an APU, tank crews could now fight in fixed positions or stay on overwatch
duties while not wasting gas. Of course, if the tank had to move, the crew could immediately
start the engine and go. But for the long hours of sitting still, an APU is required to ensure
fuel consumption is kept to a minimum. After initial test trials in Europe,
Army officials had Chrysler install an APU. However, this was not the only issue that
arose with those early tests that called into question using a gas turbine. For example,
because the engine required huge amounts of air to be sucked in through its intakes, the original
air filters weren’t advanced enough to block fine dust and debris like sand. As a result,
the initial XM-1 tanks did not function well in dry and sandy environments. While the solution was
rather simple, making better air filters, these problems caused enough of a stink with Congress
officials to order a diesel engine to be produced. Congress argued that because the Army kept finding
issues with the gas turbine engine, they needed to develop a diesel engine design
at the same time as the current design. That way, if all else was equal and the tank was
ready to enter combat minus an engine, the military could drop a trusty diesel engine in
and figure out how to implement a gas turbine one later. Fortunately for General Dynamics,
they worked through all these early issues and continued to improve on their earlier design.
Even though the APU cut down wasteful fuel consumption significantly, it still did not
help the fact that the tank was and still is very fuel inefficient. Getting just under a
mile per gallon, the Abrams is arguably one of the least fuel-efficient tanks
on the battlefield today. General Dynamics was acutely aware of this problem and began
working with Honeywell to incorporate changes in the AGT 1500 design starting in the 1980s.
During the first round of trials meant to improve fuel economy, the two companies incorporated a
number of changes. The High-Pressure turbine rotor was made more efficient and durable. A new special
coating was applied to the high-pressure turbine cylinder to prevent air leakage.
The design team changed the materials used to make the recuperator, and the power turbines
themselves were resized to ensure maximum fuel efficiency. Even so, these changes only made the
tank about 10% more fuel efficient, but that was enough. However, this was not the only development
that made the Army like the engine more. One of the main reasons that the Army chose
the gas turbine engine over a diesel one was the fact that it was digital. With computers becoming
the way of the future, Army officials knew that the best main battle tanks of the future would
be operated using computers. Because of this, the brains of the engine are in its Electronic
Control Unit. The purpose of this computer is to provide real-time fuel control to the engine
to maximize fuel efficiency. But of course, as is the case with any type of engine, it’s not immune
to breaking down. Fortunately for tank crews, Honeywell thought of a solution to that too.
Known as Turbine Engine Diagnostics or TED, the military helped develop this system during the
early 1990s. This was designed to help soldiers in the field quickly find any problems with the
engines, repair said problem, and get back into the fight as fast as possible. Because computers
could have many unseen faults associated with them, traditional methods of troubleshooting
common issues like an engine failing to start are more difficult, and TED fixed
those problems. During a feasibility study funded by the Army, soldiers from several National Guard
units were tested on their ability to diagnose what caused an Abrams’ engine not to start.
While the examiners knew what they did to cause the fault, the soldiers didn’t.
During the first trial, soldiers were asked to troubleshoot only using tech manuals and what
they previously learned in training. During the second trial, new faults were introduced,
and the soldiers were told to troubleshoot using the software. The results were better
than anything the Army could have hoped for. A breakdown of the test results showed that
among junior mechanics, TED software helped them accurately diagnose problems two to four times
as often compared to traditional methods. Even among older, more senior personnel, the
software improved their abilities to diagnose the problem by another ten percent. What this meant
for commanders in the field was that they were eliminating a lot of the guesswork that came with
troubleshooting. Instead of waiting around for a part they never actually needed, mechanics could
diagnose and fix problems much faster, meaning they could get the tank back in the fight sooner.
But providing amazing software to help troubleshoot unknown faults was
not the only thing that made the engine a dream to work with on the battlefield;
its modular design makes maintenance a breeze. Before the Abrams, most tanks that required major
engine overhauls or even needed their entire engine replaced needed to be withdrawn from
service. Instead of being in the fight, tanks would be relegated to sitting at a maintenance
depot while crews worked day and night to take the tank apart so they could get to the engine.
The AGT 1500 turned that practice on its head. This engine featured a completely modular design,
meaning that a small crew of soldiers could take out an entire engine with a crane in the field.
On average, a whole engine can get swapped out in the field in about four hours. So in a worst-case
scenario, where a commander has no desire or time to troubleshoot an engine or repair damage,
the whole thing can get swapped out for a new one while the old one gets sent back for repair.
But quick changeouts aren't the only thing the Army is interested in. Since the early 2000s, in
an initiative known as the Total Integrated Engine Revitalization or TIGER, the Army has worked hand
in hand with the defense industry to overhaul all the existing AGT 1500 engines and improve them.
These improvements included replacing older parts with newer ones that are stronger, more ergonomic,
and fuel efficient. This ongoing program means that even if the Abrams' hulls are decades old,
the engines powering them are as new as if they just came off the factory floor.
Now you need to watch “Key Weapon for Ukraine's Next Stage of War.” Or,
have a look at “Why US Enemies Are Scared of AbramsX (Next Generation Tank).”