SO how grounded in reality are the intimidating Walkers of Star Wars: The Last Jedi?

The motivation is real enough.

Armies need transport. That transport must be capable of traversing rough terrain. It must fight its way to a destination. It must protect the troops it carries.

To the untrained eye, the All Terrain – Armoured Transport (AT-AT) Walker offers all this – and more.

Overbearing. Striding. Seemingly unstoppable.

The four-legged metal monster stands about 20m tall. Its flexible head is both the vehicle’s control centre and mount for its weapons. Aboard are 40 heavily armed and armoured Imperial Stormtroopers.

It evokes exactly the sort of drama a movie director craves.

But could any of this translate to a real battlefield?

Australia’s military engineers and analysts wince when they see these metal monsters striding forth on the silver screen.

What they see are death traps.

“The AT is not the most effective design,” says ASPI Senior Analyst Dr Malcolm Davis.

The reality, of course, is that they look cool.

Director George Lucas once stated that the idea of Imperial Walkers was inspired by the terrifying Martian Tripods from H.G. Well’s seminal novel, War of the Worlds.

But on a real battlefield, intimidating looks amount to little.

Instead, the brutal experience of two World Wars, Korea, Vietnam, Afghanistan and Iraq have hammered home a multitude of lessons to Australia’s defence force and industry.

Armoured personnel carriers must be fast, manoeuvrable and responsive. They must have a low profile to remain unobserved (and not shot-at) for as long as possible. And if they are hit by enemy weapons, they must offer their human cargoes the best chance of survival.

It’s a balance of often contradictory requirements that the ADF is putting itself through again at the moment: It’s in the process of choosing a replacement combat reconnaissance vehicle under the LAND400 program.

So could an Imperial Walker ever appear in the Australian Defence Force’s line of battle?

Not if the experts of the Australian Strategic Policy Institute (ASPI) have any say on the matter.

WALKING ENGINES OF GLITTERING METAL

An AT-AT Walker lumbers along like an elephant, lifting one foot at a time. It’s a stable walking style: there’s always a ‘triangle’ of supporting legs.

It’s also slow. With a lot of stress focused on the leg joints.

“I could never figure out why Lucas went for legs on the AT ... apart from he saw it in terms being flexible across all terrains (hence the name),” says Dr Malcolm Davis.

Which is why making machines mobile on legs is not entirely ‘out there’.

The US military recently trialled a small, four-legged robotic ‘mule’ (though they gave it a cooler name — BigDog).

Its purpose was the same as that played by its fleshy predecessors: to carry food, ammunition and other supplies through rough and risky terrain to the soldiers fighting on the very front line. Like Simpson’s donkey of Gallipoli fame, the idea was also to use them to help lug the wounded back safety.

“One … if not the only … advantage of legs is that you can step over things you can’t trundle over in a tracked vehicle,” says ASPI’s Director — Defence & Strategy Program, Dr Andrew Davies. “So they would work OK in terrain with lots of obstacles … the exact opposite of an ice planet, but hey!”

So having four legs means an AT Walker could stride across rough ground, wade through shallow water, climb slopes, step over obstacles and push through undergrowth. Traditional wheeled vehicles would find all this much more challenging.

But Dr Davies points out the Imperial and First Order forces may have fallen into the trap many military engineers fear: fighting the last war over again instead of the next one.

The Empire Strikes Back battle of Battle of Hoth was on a flat, open ice plain. The Last Jedi fight appears to be on a flat, open dust pan.

Clearly, the Rebels held the tactical advantage in both cases – picking and choosing battlefields in their favour.

When it comes to the ponderous AT Walkers, that wouldn’t be hard.

Even in its evolved form, the gorilla-like AT-M6 of The Last Jedi, all of these considerations apply.

SHOCK & AWE

In real battlefield environments, says Dr Malcolm Davis, wheels or tracks offer important advantages that counter-balance the superiority of legs when crossing rough terrain.

“And given they have anti-gravity in the Star Wars universe, as evident by Like’s land speeder, why not ‘hover tanks’?” he says.

They’d be much faster. More responsive. Adaptive.

“Speed and agility would make Imperial forces much more effective and quick to close on those defensive lines of rebel troops — Leia and Han would never have made it to the Millennium Falcon, and the movie would have been over!” Dr Davis says.

Big. Brawny. Bulky.

These are real threats when applied to predators in the animal kingdom.

But not the technological battlefield.

“What happens if the ground is boggy or soft?” asks Dr Davis. “Does the AT-AT get bogged easily?”

Walkers put all their weight on just four small points of contact with the surface. Step on to soft or brittle ground – such as an ice-covered lake – and a foot will break right through.

“This is an issue that tank designers have always confronted – adding more armour to improve protection and survivability decreases mobility,” Dr Davis says.

Which is why main battle tanks use caterpillar tracks: these distribute the vehicle’s great weight across a much broader area – making what is in general a much lighter ‘footprint’.

The four-legged BigDog was ultimately rejected by the US Marines: It was simply too noisy. Wherever it went, the ‘enemy’ knew the Marines were there. And keeping it running involved too much time, effort and resources.

“One of the big disadvantages of legs is that they’re inefficient,” says Dr Andrew Davies. “The only reason that animals don’t have wheels is that there’s no way to make a bearing that rotates and that has blood vessels passing through it.”

STAND AND FIGHT

To a defence analyst, simply examining the shape of a Walker reveals several key weaknesses.

Its most vulnerable components – including its human cargo – are up high. In plain sight. Sitting in a box.

A Walker’s slab-sided body presents an easy target.

“Slab sides are to be avoided because (a) they make great targets for shaped charge rounds that penetrate and (b) they stick out like dog’s bollocks on radar,” Dr Andrew Davies says. “Angled sides (like on a stealth fighter) would be much better. The AT Walkers don’t score well on those design features!”

Tall legs lift the personnel carrier high off the ground. There’s little opportunity to hide behind terrain. And a Walker’s multitude of moving parts each present an ‘Achilles heel’ where one effectively placed blast – or entangling cable — could disable the entire machine.

“Somehow, ‘that armour is too thick for blasters’ so we use ‘harpoons’ to entangle the legs — which raises the key vulnerability of any bipedal or quadrupedal walking machine,” says Dr Malcolm Davis. “Take out one leg, the whole thing falls over.”

While the First Order has learnt something from the Battle of Hoth (it has added serrations on its Walker’s legs to sever cables), it doesn’t appear to have been enough.

And when things go wrong, Walkers don’t appear to offer much in the way of passive support for its soldiers.

Improvised Explosive Devices (IEDs) proved to be a devastating challenge to counter-insurgency operations in Afghanistan. These simple bombs, buried in roadsides, could hurl heavily armoured vehicles through the air – battering those aboard to death.

The relative success of Australian ‘Bushmaster’ armoured personnel carriers in this environment shows defence engineers had been thinking ahead.

“A ‘boat hull’ design (which you’ll find in most modern troop carriers) helps deflect blast from underneath,” says Dr Andrew Davies.

While the Stormtroopers aboard a Walker would be sitting high above any IED explosion, the AT’s legs would likely be vulnerable. It’s a long way down. Their crash-couches would have to be extremely effective.

It’s obviously not a scenario the Walker’s overconfident designers or Imperial procurement officers anticipated.

TOOTHLESS TERROR

Thick slabs of metal. Lots of big guns.

Surely an AT-AT would be a fearsome killer, if not a safe place to be?

Not so say ASPI’s analysts.

“The modern Russian T-14 Armata main battle tank has an ‘active denial’ system which is designed to defeat anti-tank guided weapons before they can reach the tank,” Dr Malcolm Davis says. “Yet even though the Imperial Empire has the Death Star, they don’t appear to have shields on their AT-ATs. So if we were going to build a real AT-AT, it would have at the very least an ‘active denial system’.”

On Earth, as opposed to a galaxy far, far away, that involves a suite of finely tuned sensors. These detect incoming missiles, quickly compute the trajectories – and rapidly fire point-defence guns and missiles against them.

We’ve seen no evidence of this on the silver screen when it comes to Walkers.

But they do have big, fearsome ‘heads’ – bristling with cannon.

Staring an AT Walker in the face would be a terrifying – and short – experience.

And it would also give the Imperial gunners an advantage: In the Star Wars universe, ‘blasters’ travel in straight lines. Projectile guns like those on modern tanks ‘lob’ due to the effects of gravity. So an elevated vantage point gives the AT a broad view – and greater reach — over the battlefield.

This benefit would also apply to the huge cannon strapped to the back of the new AT-M6.

But, in both cases, any Rebel insurgents would need only move to the sides or behind to overcome get out of their reach.

“The AT is poorly armed — with guns only pointing forward, below a vulnerable crew compartment,” says Dr Davis. “So the AT can only attack on one front — and must move its head completely to target the weapons.”

Efficiency, again, is seriously lacking.

“A better system would be turreted weapons and on a large vehicle like the AT, you could have a lot of turrets with laser weapons able to shoot down snowspeeders,” he says.

Dr Davis says the most ‘realistic’ science fiction armoured warfare weapon he has encountered are the “Bolo” tanks which appear in novels by Keith Laumer.

“A Bolo is a very large, AI-based, self-aware robotic tank that would make short work of ‘that rebel scum’,” he says.