The Insane Engineering of the M1 Abrams

Last updated: May 7, 2023

The M1 Abrams tank uses a special turbine engine that makes it faster and lighter than tanks that use diesel engines.

This engine can also run on a variety of fuels and has a high torque advantage. The tank's armor has evolved over time and now uses a combination of ceramic and metal plates to protect against projectiles.

The armor also includes a layer called a spall liner that limits damage caused by shock waves. Finally, the M1 can use reactive armor tiles to further protect against shaped charges.

  • The M1 Abrams tank uses a high-speed turbine engine that is lighter and faster than diesel engines.
  • The engine has a high torque advantage and can run on many fuel types.
  • The tank's armor uses a special ceramic and metal composite that is highly effective at protecting against projectiles.
  • The armor includes a spall liner that limits damage from shock waves.
  • Reactive armor tiles can be added to the tank to protect against shaped charges.
  • The exact details of the armor's composition and thickness are classified
  • The M1 Abrams has two smoke generating systems - engine exhaust injection and grenade launchers.
  • The tank has a dedicated crew member, the loader, for manual loading.
  • German Rheinmetall RH-120 is used in the tank's 120 mm guns.
  • The M1 Abrams weighs between 52 and 68 tonnes.
  • The tank has a torsion spring suspension system.
  • Hydrogas suspensions were considered during development.

Turbine Engine Advantages 02:05

  • The M1 Abrams uses a high-speed turbine engine.
  • Turbine engines are typically used in aircraft, but the M1 uses it to give two significant advantages.
  • Turbine engines are lighter than diesel engines, giving the M1 a weight advantage.
  • The M1 can stack on layers of armor without affecting its speed or acceleration.
  • The turbine engine has a massive torque advantage at lower shaft speeds.
  • The M1 can run on most fuel types, making it easier to procure fuel in a warzone, and come with the added bonus of helping the M1 Abram operate in hot or cold weather.
  • The turbine engine is not connected to the compressors, which run things like compressors, electronics, and hydraulics.
  • This primary drive shaft and its reduction gearbox are surrounded by something called a recuperator.

The Recuperator 05:51

  • The recuperator is a giant heat exchanger that lowers the heat signature of the exhaust and increases fuel efficiency, transferring more heat energy back into the engine instead of losing it to the atmosphere.
  • The M1 Abrams is still a thirsty machine, even by tank standards.
  • The turbine engine uses twice the fuel as a comparable diesel per kilometer.
  • The armor installed on the M1 Abrams has evolved and changed over the last four decades.
  • The exact details of its thickness, location, materials, and layering are classified for obvious reasons.

Composite Ceramic Armor 07:27

  • Early M1 variants used a type of composite ceramic armor called Chobham.
  • Chobham derives much of its ballistic resistance from an extremely hard and light ceramic layer.
  • Hardness in material science is a measure of a material's ability to resist localized deformation, like a scratch.
  • Diamonds are extremely hard, and because of this, industrial diamonds are coated onto cutting tools to help them cut through materials without being eroded themselves.
  • A hard material can scratch and erode a softer material.
  • Hardness can be measured with a Vickers hardness test, which pushes a pyramid-shaped diamond into the material.
  • The hardness is then calculated by dividing the force applied resulting surface area of the indentation.
  • The rolled homogeneous armor steel of World War II has a Vickers Hardness of 380, high carbon hard steel is about 550, while a ceramic like silicone carbide offers hardness 5 times greater, up to 2500.
  • Ceramics are extremely brittle, and they shatter into a million pieces with little force.

Ceramic Composite Armor 08:44

  • Ceramic composite armor combines ceramic and metal to create a highly effective armor system.
  • The ceramic is placed on the outside of metal plating, acting like an extremely hard outer shell.
  • When a round strikes the armor, the compressive strength and hardness of the ceramic coating causes the round to fracture and break apart, at the same time ceramic coating begins to fracture and fragment, spreading the energy of impact across a larger area which is then absorbed by the tougher metal plate backing ceramic.
  • Ceramic armor performed even better when placed under compression.
  • This can be achieved by simply adding a face plate and bolting the two pieces together.
  • Embedded compressed ceramic armor can defeat kinetic energy weapons.

Spall 10:48

  • Projectiles don’t necessarily need to penetrate every layer of armor to be deadly.
  • If they hit with enough force, the kinetic energy can simply transfer through the material as a wave and cause material on the inside of the tank to turn into deadly shrapnel inside the crew compartment.
  • This is called spall.
  • High explosive squash heads are made from soft plastic explosives that spread out over the armor's surface.
  • The spall liner is a ductile and dense material that limits spalling.
  • For early M1s, this layer was typically composed of lead, but beginning in 1988 certain M1A1s began to be upgraded with depleted uranium spall liners.
  • And all new M1A2s were assembled with depleted uranium liners.
  • Modern composite armor makes it difficult for this shock wave to transmit through the material, and a spaced layer with an air gap can defeat this squash head munition completely.

Reactive Armor 12:14

  • Reactive armor is particularly effective at dealing with shaped charges.
  • Shaped charges consist of a charge shaped with a hollow indentation, lined ductile metal liner.
  • When the charge is detonated, a pressure wave forms behind this metal liner, deforming it and accelerating the metal into a lance stream of particles.
  • The shaped charge effectively creates a hypersonic projectile at point-blank range.
  • Reactive armor works by placing an explosive charge between two metal plates.
  • When a jet from shaped charge strikes the upper plate, it detonates inner explosive.
  • The outer plate then flies outwards to disrupt the incoming jet while a shockwave formed by the detonation also breaks up the stream of metal approaching the tank.
  • Additional reactive armor tiles can be added to the outside of the M1 too.

Smoke Screen 13:16

  • The M1 has two systems for generating smoke to conceal itself in an engagement.
  • The first involves simply spraying fuel into the engine exhaust, which vaporizes and creates a large opaque cloud behind the tank.
  • However, it’s extremely important that the driver remembers which fuel tank is running on.
  • The second system uses grenade launchers mounted on the outside of the turret.
  • These launchers are controlled from the tank commander's seat.
  • There are two versions that the M1 uses.
  • The 8 canister M257 typically used with US Marine Corps M1s, and the more widely 6 can M250.
  • Launching them about 30 meters from the tank provides a shrouding curtain of smoke to hide its movements.

Crew and Loader 14:27

  • The engineers of the M1 Abrams did everything in their power to make it as survivable as possible, protecting the crew inside.
  • 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 Russian tanks; however, the USA has shunned them in their tanks, seeing an autoloader as an unnecessarily complex mechanism that would impact the M1s reliability.
  • The loader enters the tank through the turret hatch, sitting to the left of the main gun with access to the ammunition box behind them.
  • The gunner on their right is in charge of aiming at targets using these day and thermal night vision sights, along with a laser range finder to input target distances into the ballistics computer.
  • When instructed by the tank commander, sitting behind the gunner, the loader will press a switch with their knee to open a hydraulically actuated armored door behind them.
  • The tank commander will specify the round needed, and the loader will take it out, load it into the breach, close the breach, and move the safe handle to the armed position.

Standardization challenges 16:36

  • With the development of depleted uranium rounds, the 105 mm gun on the previous generation M60 tank was viewed as inadequate to deal with any Soviet armor.
  • The US allies, like Germany, did not want to use depleted uranium rounds due to ethical implications. They were moving towards using 120 mm cannons with the British Chieftain tank using the Royal Ordinance L11 and the German Leopard 2 Rheinmetall RH-120.
  • This posed a problem for NATO’s goals of standardizing wherever possible to optimize logistics.
  • With ammunition factories across NATO countries producing the same ammunition, this ensured ammunition could not only be shared but also manufactured as close to the frontline as possible.
  • The M1 Abrams uses 120 mm guns that are German Rheinmetall RH-120 manufactured under license in the US.

The M1A1 and M1A2's cannon 17:23

  • The cannon is 5.3 meters long and weighs 3.3 tonnes.
  • The large bulge in the middle of the cannon is designed to help evacuate barrel propellant gasses after each firing.
  • Atmospheric pressure can prevent gasses from leaving once the round leaves the barrel, and once the breach is opened, potentially harmful explosive gas can enter the crew compartment.
  • The bore evacuator is a simple solution with holes that allow gasses to enter the evacuator as the round passes by.
  • This acts like a pressure reservoir.
  • When the round leaves the barrel with this attachment, pressure is released from forward-facing holes at the far end of the evacuator that pushes remaining gas outwards.

Rounds used by the M1 18:05

  • The two primary rounds used by the M1 are M829 Depleted Uranium round, which is a saboted kinetic energy round, and the M830A1 HEAT Round, which does not use heat as part of its offensive.
  • The M830A1 HEAT Round uses a kinetic energy shaped charge.

Weight and suspension system 18:24

  • The M1 Abrams is a heavy vehicle, weighing between 52 and 68 tonnes depending on the generation configuration.
  • The armor, cannon, engine, and ammunition make this an extremely heavy vehicle.
  • The M1 Abrams needed a track and suspension system capable of bearing that weight.
  • For a vehicle this heavy, typical helical springs have some problems.
  • The torsion springs of the M1 are located inside the hull and raise the hull height by 150 millimeters.
  • The torsion springs of the M1 run along the width of the hull, making them quite heavy.
  • Torsion bars are very easy to swap out when they aren't broken, but if bent or shattered, or if the body of the tank is bent, it can be difficult to pull long torsion springs out.
  • Modern tanks are increasingly moving towards hydrogas suspensions.

Torsion springs vs. hydrogas suspensions 21:41

  • Hydrogas suspensions are much smaller, lighter, and easier to service than torsion bars.
  • The road wheel has an attached axle pivot arm, which in turn turns a crank and con-rod piston.
  • This piston connects to the hydragas suspension cylinder.
  • The first chamber is filled with fluid, typically oil.
  • The oil is relatively incompressible and provides marginal spring force, but this chamber has a damper valve that serves to restrict the transfer of fluid between this chamber and the next, which contains a floating piston with compressed nitrogen gas on the other side.
  • This provides resistance to ensure the road wheels stay in contact with the ground but also dampens out vibrations.
  • Hydrogas suspensions were considered for the M1 during development, but it was a relatively new technology at the time, and so torsion spring was chosen.

Incremental improvements of the M1 Abrams 22:49

  • The M1 Abrams has had incremental improvements added over the past four decades.
  • With three primary variants, the M1, M1A1, and M1A2, with even more specialized iterations in between.
  • Updated sensors and controls have brought the tank into the 21st century, like the Crows II on M1A2 SEP.
  • SEP standing for systems enhancement package.
  • The M1A2 SEP V4 variant is currently in use, and the army is considering the future of the M1 program, whether that’s an M1A2 SEP V5 or a completely new platform.

Introduction 23:41

  • The M1 Abrams is one of the longest-serving tanks in modern military history, having served for over four decades.
  • Despite its age, it is still highly capable and a valuable asset to troops on the ground in conflicts such as Ukraine.

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