The Development and Evolution of Main Battle Tanks: A Look at the M1 Abrams

The M1 Abrams is one of the longest-serving main battle tanks in modern military history, with over four decades of service. Its development was influenced by various factors, including the need for a more rigidly mounted torsion bar to develop spring force. To achieve this, two torsion bars were mounted alongside each other, creating an offset in distance between the two sides of the tracks. This design allowed the tank to absorb bumps and vibrations, providing a smoother ride for the crew.

However, this design also had its drawbacks. The leading road wheel would hit bumps first, absorbing more force than the trailing road wheel. This resulted in increased wear on the leading torsion spring, necessitating more frequent replacement. Torsion bars are relatively easy to swap out when they're not broken, but if bent or shattered, or if the body of the tank is bent, it can be difficult to pull the long torsion springs out.

In recent years, modern tanks have increasingly moved towards hydrogas suspensions, which offer several advantages over traditional torsion bars. The road wheel has an attached axle pivot arm, which in turn turns a crank and connects to a piston. This piston connects to the hydragas suspension cylinder, which contains a fluid that provides marginal spring force. A damper valve restricts the transfer of fluid between this chamber and the next, which contains a floating piston with compressed nitrogen gas on the other side. This setup provides resistance to ensure the road wheels stay in contact with the ground while also damping out vibrations.

The use of hydrogas suspensions has several benefits over traditional torsion bars, including being smaller, lighter, and easier to service. It also lowers the height of the tank, reducing its profile and making it harder to hit. Additionally, each individual suspension can be remotely adjusted by changing the gas pressure inside the cylinder, allowing the tank to take a crouched position if needed.

During development, the M1 Abrams considered using hydrogas suspensions, but they were still a relatively new technology at the time. As a result, the torsion spring was chosen as the primary suspension component. Over the years, however, incremental improvements have been made to the design, including three primary variants: the M1, M1A1, and M1A2. Even more specialized iterations, such as the M1A2 SEP (Systems Enhancement Package), have been developed.

The M1A2 SEP variant features additional thermal sights for the tank commander, an auxiliary power unit to run its electronics without running the fuel-hungry engine, and the CROWS II controller, a remote control sight that allows the tank commander to operate the gun from the safety of the turret. The army is currently considering the future of the M1 program, with potential variants including the M1A2 SEP V4 and a completely new platform.

Despite its age, the M1 Abrams remains highly capable and will continue to be an asset to troops on the ground. Its ability to adapt to changing situations and absorb vibrations makes it an ideal choice for modern military operations. The next episode of Real Engineering explores the incredible physics behind magnetic resonance imaging (MRI), which uses a similar property innate to our body tissues – the quantum spin of hydrogen atoms.

Understanding quantum mechanics is becoming increasingly relevant in everyday engineering, from MRI machines to quantum computing. Brilliant offers three courses to help you get started with understanding this scientific concept. The platform provides interactive lessons that make it easy to jump in and out of courses, allowing you to learn on your own time. With their mobile app, you can even learn the fundamentals of computer science during your morning commute.

Brilliant includes interactive elements to help you quickly understand concepts and test your knowledge along the way. The platform focuses on facilitating effective education that will help you progress in your learning goals, whether it's professional career advancement or just for fun as a lifelong learner. With new content added monthly, there's always something new to learn. You can get started for free for the first 30 days by clicking the link on screen now, and the first 500 people to do so will receive 20% off Brilliant's annual premium subscription.

In conclusion, the M1 Abrams is a testament to the evolution of main battle tank design. From its early development with torsion bars to the current hydrogas suspensions, each iteration has improved the tank's capabilities and reduced its profile. As we move forward in the future, it will be exciting to see how modern engineering continues to shape the M1 Abrams and other military hardware.

"WEBVTTKind: captionsLanguage: enThe M1 Abrams entered service in 1980.A fast, heavily armored tank with the verylatest technologies to give it every advantageon the battlefield.First seeing action in Operation Desert Storm.The plain arid camouflaged tank gained a reputationquickly in the barren deserts of Saudi Arabiaand Kuwait.Powered by a high speed turbine engine, theM1 raced across this difficult terrain toliberate Kuwait from Iraqi occupation.The german designed 120 mm smoothbore cannonhad longer range, more accurate fire and moreadvanced ammunition.It easily dispatched the lower tech sovietsupplied tanks of the Iraqi ArmySometime this year it’s expected that theUS will deliver a battalion of 31 M1 Abramtanks to Ukraine to once again face off againstthe Soviet tanks it was designed to battle.The Ukrainian Army will need training to maintainand operate these new tanks, because it’sunlike any other tank.And although this tank are over 40 years oldit's still more than capable of holding itsown on the battlefield, thanks to continualmodernisation and forward thinking design.This is the insane engineering of the M1 Abrams.The M1 Abrams, upon engine start up, soundsmore like a military aircraft getting readyto take off.*minor pause 1-3 seconds to allow sound tobe heard*A terrifying increasing pitch as the enginerevs up to speed.The whirring sound emanating from the rotatingturbine blades hidden inside.The turbine engine, typically used for jetaircraft, is an engine designed for high speedoperation with minimal weight, a counter intuitivechoice for a heavy battle tank.So why was it chosen?The turbine engine would give the M1 two hugeadvantages.They are much lighter than an equivalent dieselengine, weighing just 1.1 tonnes, developing1500 brake horsepower.The V12 diesel engine of the Challenger 2produces just 1200 brake horsepower with 2tonnes of metal.This compactness and extreme high power toweight ratio allows the M1 to stack on layersof armor without sacrificing accelerationor top speed.We can plot torque vs shaft speed of the HoneyWellAGT1500 turbine engine of the M1 against theV12 MTU 883 of the Challenger 2E, and we cansee the turbine has a massive torque advantageat lower shaft speeds.In its lightest configuration M1 weighs 61.8tonnes.A typical toyota corolla weighs 1.1 tonne.That’s equivalent to 56 Toyota Corollas,yet this thing can still accelerate from 0-32kilometers per hour in just 7 seconds witha top speed of 72 kilometers per hour.The M1 Abrams primarily uses diesel fuel,as diesel can act as an additional layer ofarmor.Liquids are extremely good at absorbing energyfrom explosions and kinetic energy weapons,they are most effective against shaped charges,and tanks carry a lot of liquid in the formof fuel.It may seem counterintuitive to use a fuelas protection from an explosion, but dieselfuel is not very flammable.In fact if you throw a lit match into a puddleof diesel it will put out the match.Diesel engines require immense pressure anda sustained flame to ignite.Because of this diesel can actually be usedwith relative safety as armor.However the turbine engine can also operateon most fuel types.This is a huge advantage in military logistics.Making joint operations with NATO vastly easier.In the years following World War 2.The Soviets favored diesel compression ignitionengines.The western Allies used a mixture of bothgasoline spark ignition and diesel compressionignition.Transporting fuel is one of the largest logisticchallenges in war.Needing several types of fuel makes it allthe more difficult.The M1 can run on marine diesel, gasolineor even kerosene if needed.Which not only makes it easier to procurefuel in a warzone, but comes with the addedbonus of helping the M1 Abram operate in hotor cold weather.Dealing with the wild swings in temperaturethat Ukraine can expect throughout the yearwith ease.Where diesel fuels can crystallize at lowtemperatures, kerosene can be used instead.The turbine engine of the M1 works similarlyto aircraft jet engines, with some importantdifferences.Air enters the engine here, where it is compressedby the low pressure compressor, and then thehigh pressure compressor, each individuallydriven by separate turbine stages.These turbine stages are driven by the combustor,which works a little differently to typicalaircraft combustors.It is mounted perpendicularly to the engine,and protrudes out of the engine.This makes maintenance access to the combustoreasier, with only a simple bolted cover needingto be removed.There are two drive shafts in this engine.A secondary drive shaft, driven by the highpressure turbine, which runs forward to anaccessory gearbox that runs things like compressors,electronics and hydraulics.The main drive shaft, driven by a dedicatedpower turbine, which is not connected to thecompressors, runs rearward to the tanks drivesprockets.This primary driveshaft and its reductiongearbox is surrounded by something calleda recuperator.This is the biggest difference between thisturbine engine and a typical aircraft jetengine.We don’t want the hot exhaust of the enginespewing out like a jet engine, the heat signaturethis would create would be a giant beaconfor heat guided missiles and give the tankslocation to any enemy using thermal vision.We also don’t want to waste all that heatenergy.The recuperator is essentially a giant heatexchanger.Air coming from the compressor stage is passedthrough it, where it is heated by the exhaustbefore entering the combustion chamber.This lowers the heat signature of the exhaustand increases fuel efficiency, transferringmore heat energy back into the engine insteadof losing it to the atmosphere.But the M1 Abrams is still a thirsty machine,even by tank standards.The turbine engine uses twice the fuel asa comparable diesel engine per kilometer.Where the M1A1 consumes around while cruisingat 40 kilometers per hour, the Leopard 2 consumes2.2 liters per kilometer.But the US military deemed this issue a costworth paying for the capabilities the turbineengine provided.Allowing the M1 to carry an obscene amountof armor, while keeping its acceleration high.The armor installed on the M1 Abrams has evolvedand changed over the last 4 decades.The exact details of its thickness, location,materials and layering is classified for obviousreasons, but there is a great deal known aboutthe science and nature of its armor.It is well publicized that early M1 variantsused a type of composite ceramic armor calledChobham.Which derives much of its ballistic resistancefrom an extremely hard and light ceramic layer.Hardness in material science is a measureof a material's ability to resist localizeddeformation, like a scratch.Diamonds are extremely hard, and because ofthis industrial diamonds are coated onto cuttingtools to help them cut through materials,without being eroded themselves.A hard material can scratch and erode a softermaterial.Hardness can be measured with a vickers hardnesstest, which pushes a pyramid shaped diamondinto the material.The hardness is then calculated by dividingthe force applied by the resulting surfacearea of the indentation.The rolled homogeneous armor steel of worldwar 2, has a Vickers Hardness of 380, a highcarbon hard steel is about 550, while a ceramiclike silicone carbide offers a hardness 5times greater, up to 2500 While beingmuch lighter than steel.Making it an excellent candidate for armor.But, anyone that has dropped a dinner plateknows that ceramics are extremely brittle.They shatter into a million pieces with littleforce,but this can be used to the tanks advantagewhen combined with a tougher metal backingplating.In this configuration the ceramic is placedon the outside of the metal plating, actinglike an extremely hard outer shell.When a round strikes the armor the compressivestrength and hardness of the ceramic coatingcauses the round to fracture and break apart,at the same time the ceramic coating beginsto fracture and fragment, spreading the energyof impact across a larger area which is thenabsorbed by the tougher metal plate backingthe ceramic.Tough in material science meaning it can absorba lot of energy without fracturing, the oppositeof brittle.Further research and experimentation foundthat ceramic armor performed even better whenplaced under compression.This can be achieved by simply adding a faceplate and bolting the two pieces together.This changes the dynamics of an impact significantly,and helps immensely with resisting attackfrom long-rod kinetic energy projectiles.These are rounds specifically designed asanti-armor weapons.They are thin, long dart-like projectilesthat require a sabot to launch out of tankbarrels.They are typically manufactured from highdensity materials like Tungsten.With a thin aerodynamic shape and high density,these weapons have an extremely high ballisticcoefficient, allowing them to ram into targetsat a distance at high velocities.They can obliterate rows of concrete wallswith ease.Embedded compressed ceramic armor can defeatthese kinetic energy weapons.When the long rod projectile strikes the faceplate it sends a pressure wave through theceramic that pulverizes it and increases itsvolume.This creates what is essentially an abrasivemaze of extremely hard and sharp particlesthe penetrator has to push through, graduallygrinding it away.Computer simulations of this effect show thatthe harder the material the better.This is the magic of ceramic composite armor.On top of these metal and ceramic layers thereis typically a very dense inner liner calleda spall lining.Projectiles don’t necessarily need to penetrateevery layer of armor to be deadly.If they hit with enough force the kineticenergy can simply transfer through the materialas a wave and cause material on the insideof the tank to splitter and turn into deadlyshrapnel inside the crew compartment.This is called spall.Some munitions are specifically designed tocause this.High explosive squash heads are made fromsoft plastic explosives that spread out overthe armor's surface.With the increased surface area and directcontact with the armor, the explosion transfersa great deal of energy through the materialand blows out the armor's backing.This works by sending a compressive shockwave through the material and reflects andrebounds inside the material, creating regionsof intense stress that fractures the armor.The spall liner is a ductile and dense materialthat limits spalling.For early M1s this layer was typically composedof lead, but beginning in 1988 certain M1A1s,began to be upgraded with depleted uraniumspall liners, which are even denser than lead.And all new M1A2s were assembled with depleteduranium liners.However, modern composite armor makes it difficultfor this shock wave to transmit through thematerial and a spaced layer with an air gapcan defeat this squash head munition completely.Additional reactive armor tiles can be addedto the outside of the M1 too.Reactive armor is particularly effective atdealing with shaped charges.Shaped charges consist of a charge shapedwith a hollow indentation, lined with a ductilemetal liner.When the charge is detonated a pressure waveforms behind this metal liner, deforming itand accelerating the metal into a lance streamof particles.The shaped charge effectively creates a hypersonicprojectile at point black range.It’s highly effective at cuttingthrough armor.Reactive armor works by placing an explosivecharge between two metal plates.When a jet from a shaped charge strikes theupper plate it detonates the inner explosive.You may think this could damage the tank,but tank’s lower armor is more than capableof dealing with the relatively blunt pressureformed by the reactive armor detonation.The outer plate then flies outwards to disruptthe incoming jet while the shockwave formedby the detonation also breaks up the streamof metal approaching the tank.Ofcourse, the best defense is to not be hitat all, and the M1 can create a smoke screenfor itself when needed.The M1 has two systems for generating smoketo conceal itself in an engagement.The first involves simply spraying fuel intothe engine exhaust, which vaporises the fueland creates a large opaque cloud behind thetank.However it’s extremely important that thedriver remembers which fuel the tank is runningon.This works for diesel fuel, but if gasolineor kerosene is used it won’t conceal theM1, it will set it on fire.The second system uses these grenade launchersmounted on the outside of the turret.There are two versions that the M1 uses.The 8 canister M257 typically used with USMarine Corps M1s, and the more widely used6 can M250.These launchers are controlled from the tankcommander's seat here.Pressing 1 button launches 6 grenades, 3 fromthe left and right side.Pressing both buttons launches all 12 of thegrenades.Launching them about 30 meters from the tankand providing a shrouding curtain of smoketo hide it’s movements.The engineers of the M1 Abrams did everythingin their power to make the M1 as survivableas possible, protecting the crew inside.And the highly trained crew are the most importantpart of this machine.The M1 Abrams does not have an automatic loader,like many modern tanks.It has a dedicated crew member, the loader,to load rounds into the breach.Autoloaders are a feature of modern Russiantanks, however the USA has shunned them intheir tanks, seeing an autoloader as an unnecessarilycomplex mechanism that would impact the M1sreliability.Seeing a forth crew member, capable of keepingwatch, maintaining the vehicle and takingover responsibilities in an emergency as anadvantage, not a disadvantage.The loader enters the tank through the turrethatch, sitting to the left of the main gunwith access to the ammunition box behind them. The gunner to their right is in charge ofaiming at targets using these day and thermalnight vision sights, along with a laser rangefinder to input target distances into theballistics computer.When instructed by the tank commander, sittingbehind the gunner, the loader will press aswitch with their knee to open a hydraulicallyactuated armored door behind them.The tank commander will specify the roundneeded and the loader will take it out andload it into the breach, close the breachand move the safe handle into the armed position.This process will be repeated until a ceasefireis called by the tank commander.The armored ammunition access door is onlyopen when loading, and this is crucial forthe survivability of the M1 Abrams.If a round penetrates the ammunition box itcan result in a lethal detonation of the ammunitionstored inside.This armored door is capable of withstandingthis blast, and panels on top of the tank,called blow out panels, are designed to breakand allow the pressure and heat to be directedupwards and away from the crew.These rounds are fired out of the M1s 120mm cannon.Early M1s were fitted with a 105 mm cannon.105 referring to the bore diameter of thegun.This decision was made primarily to allowa sharing of ammunition and parts betweenthe 105 mm on the previous generation M60tank.With the development of depleted uranium roundsit was viewed that this gun was more thanadequate to deal with any soviet armor.However US allies like Germany did not wantto use depleted uranium round due to ethicalimplications, and were moving towards 120mm cannons with the British Chieftan tankusing the Royal Ordanance L11 and the GermanLeopard 2 using the Rheinmetall RH-120.This posed a problem for NATO’s goals ofstandardizing wherever possible to optimizelogistics.With ammunition factories across NATO countriesproducing the same ammunition, this ensuredammunition could not only be shared, but manufacturedas close to the frontline as possible.The 120 mm guns of the M1A1 and M1A2 are infact the German Rheinmetall RH-120 manufacturedunder license in the US.A 5.3 metre long, 3.3 tonne smooth bore cannon.This large bulge in the middle of the cannonis designed to help evacuate the barrel ofpropellant gasses after each firing.Once the round leaves the barrel atmosphericpressure can prevent the gasses from leaving,and once the breach is opened the potentiallyharmful and explosive gas can enter the crewcompartment.The bore evacuator is a pretty simple solution,with holes that allow gasses to enter theevacuator as the round passes by.This acts like a pressure reservoir.When the round leaves the barrel with thisattachment, the pressure is released fromforward facing holes at the far end of theevacuator that pushes the remaining gas outwards.The two primary rounds used by the M1 arethe M829 Depleted Uranium round, which isa saboted kinetic energy round, and the M830A1HEAT Round, which, despite its name, doesnot use heat as part of its offensive.It uses a kinetic energy shaped charge.We have been piling on weight in this vehicle.The armor, cannon, engine and ammunition makesthis an extremely heavy vehicle.Weighing between 52 and 68 tonnes dependingon the generation and configuration.The M1 Abrams needed a track and suspensionsystem capable of bearing that weight.For a vehicle this heavy typical helical springshave some problems.First, their maximum travel is limited.At a particular load the layers of a helicalspring will meet and no further travel ispossible, bottoming out and providing an extremelyuncomfortable ride for the crew.To deal with a heavier vehicle we need toincrease the spring coil diameter, takingup an increasing amount of space.This was an issue for world war 2 era tanks,with the M4 Sherman opting to use a volutespring, which is a conical spring that iscapable of compressing to a much smaller sizeas the sheets of spring steel overlap.However most modern tanks utilize the torsionsprings, which take up very little space insidethe tank, though they do raise the tanks heightconsiderably.The torsion springs of the M1 are locatedhere, and because they are inside the hullthey raise the hull height by 150 millimeters.The road wheel is attached to a lever thatcan travel up and down, this lever arm isattached to the torsion bar so that it twistswhen the lever arm moves up and down.The spring force is derived from the barsresistance to torsion.Older tanks incorporating torsion bars hadlimited travel.The M1’s predecessor, the M60, had a wheeltravel of just 20 centimeters.During development of the M1 the two tankswere pitted against each other, with the M1benefiting from 20 years of material scienceprogress, its max travel was nearly doublethat of the M60 at 38 centimeters.When tested on a track with a series of 30centimeter bumps at 32 kilometers per hour.The M60 managed to break its front front wheels,lost control, and broke the drivers arm.The torsion spring of the M1 runs along thewidth of the hull.Making them quite heavy.We need the torsion spring to be as long aspossible because the travel distance is afunction of the torsion bar's length.Longer torsion bars can twist more beforebreaking.An interesting quirk of the torsion springsystem is that typical designs, like the M1’s,mean that the road wheels cannot be aligned.We cannot simply connect the lever arms ofopposite road wheels to the same torsion spring,as they would frequently travel together,creating no torsion.The far end of the bar needs to be rigidlymounted to the body of the tank in order todevelop a spring force.So two torsion bars need to be mounted alongsideeach other, creating an offset in distancebetween the two sides of the tracks.The two sides of the M1 are not symmetrical.This comes with some drawbacks.The leading road wheel will hit bumps first,meaning it will absorb more force than thetrailing road wheel.Increasing the wear on the leading torsionspring, resulting in more frequent replacement.Torsion bars are very easy to swap out whenthey aren’t broken, but if bent or shattered,or if the body of the tank is bent, it canbe difficult to pull the long torsion springsout.Modern tanks are increasingly moving towardshydrogas suspensions.Which look like this.The road wheel has an attached axle pivotarm, which in turn turns a crank and con-rodpiston.This piston connects to the hydragas suspensioncylinder.The first chamber is filled with a fluid,typically oil.The oil is relatively incompressible, andso provides marginal spring force, but thischamber has a damper valve that serves torestrict the transfer of fluid between thischamber and the next, which contains a floatingpiston with a compressed nitrogen gas on theother side.This provides resistance to ensure the roadwheels stay in contact with the ground, butalso dampens out vibrations.This system is much smaller, lighter and easierto service than a torsion bar, while loweringthe height of the tank, lowering its profileand making it harder to hit.Not only that, but each individual suspensioncan be remotely adjusted by changing the gaspressure inside the cylinder.Allowing the tank to take a crouched positionif needed.Hydrogas suspensions were considered for theM1 during development, but it was a relativelynew technology at the time, and so the torsionspring was chosen.The M1 Abrams has had incremental improvementsadded over the past 4 decades.With three primary variants the M1, M1A1 andM1A2, with even more specialized iterationsin between.With updated sensors and controls to bringthe tank into the 21st century.Like the Crows II on the M1A2 SEP.SEP standing for systems enhancement package.Which added additional thermal sights forthe tank commander, an auxiliary power unitto run it’s electronics without runningthe fuel hungry engine, and the CROWS II controller.A remote control sight that allows the tankcommander to operate the gun from the safetyof the turret.We are currently on the M1A2 SEP V4 variant,and the army is considering the future ofthe M1 program, whether that’s an M1A2 SEPV5, or a completely new platform, but makeno mistake, despite the M1 being one of longestserving tanks in a modern military, over 4decades old it’s still highly capable andit will be a massive asset to the troops inthe ground in Ukraine.The next episode of Real Engineering is aboutthe incredible physics behind magnetic resonanceimaging.It will be out on YouTube in 2 weeks, butmaybe you want to prepare in advance to betterunderstand what we talk about.MRI machines use a pretty incredible propertyinnate to our body tissues, the quantum spinof hydrogen atoms and how they interact indifferent tissue types.It took us a long time to write this script.Understanding quantum mechanics is hard, andquantum physics is becoming increasingly relevantin everyday engineering.From magnetic resonance imaging to quantumcomputing, Brilliant has 3 courses to getyou started with understanding this scientificconcept.It’s powerful knowledge to obtain, and youcan complete a course for free by signingup at brilliant.org/realengineering.Getting started on your first course is completelyfree for the first 30 days, but the first500 people that sign up with our link willget 20% off Brilliant's annual premium subscription.Brilliant makes learning fun and interestingwith bized-sized interactive lessons thatmake it easy to jump in and out of courses,so you can learn on your own time, and it’seven easier with their mobile app, so youcan learn the fundamentals of computer scienceon your morning commute to work or school.Brilliant includes interactive elements tohelp you quickly understand concepts, andtest knowledge along the way to ensure youare understanding the concepts you are learning.Brilliant focuses on facilitating effectiveeducation that will help you progress in yourlearning goals, whether it's professionalcareer advancement, or just for fun for lifelonglearners.Brilliant are adding content monthly, so there’salways something new to learn.You can get started for free for the first30 days by clicking the link on screen now,and the first 500 people to do so will get20% off Brilliant's annual premium subscription.\n"