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Premise: My setting incorporates an alternate history with a Martian invasion at the end of the 19th century as in War of the Worlds, the two major technical differences being that the Martians are not immediately incapacitated by endemic earth diseases and human warmaking is slightly more advanced along vaguely steampunkish lines (larger airships, earlier tanks, etc...).

To make the Martians tactically more flexible, I assume they have a wider variety of weaponry than direct-fire beam weapons (heat rays) and indirect-fire gas canisters (black smoke), including explosive-tipped guided missiles (typically called buzz-bombs by the human defenders). Assume the buzzbombs were originally developed for use against other Martian warcraft (i.e. tripods, 'flying machines') and perhaps Barsoomian-type contragravity aeronefs.

Question: How well would the guided buzz-bombs perform against early aircraft, such as hot air balloons, early airships (rigid or non-rigid), and early airplanes? My thought is that they would not be well-suited against many early aircraft with the possible exception of large zeppelins because their largely wood and canvas construction, smaller size, and cooler engines would render them harder to detect. I searched for Radar Cross Sections of WWI aircraft, but nothing turned up.

(Earth's higher gravity, thicker atmosphere, and warmer air would also affect performance of the Martian weapons, but ignore this for the time being).

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    $\begingroup$ Infrared signatures would still be a viable way to target. Given the flimsy-ness of those aircraft and their low velocity, I can't see them lasting very long. And remember, the zeppelins were using hydrogen....that isn't ideal. $\endgroup$ – kingledion Jan 3 '18 at 16:20
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    $\begingroup$ Given the speed of early aircraft they would be incredibly vulnerable to the heat rays that a martian craft would be armed with. $\endgroup$ – sphennings Jan 3 '18 at 16:32
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    $\begingroup$ Let's agree to disagree on that, then. In any case, the question is about how well PGMs would work against early aircraft, not about how successful early aircraft would be in opposing the invasion. $\endgroup$ – Mike DiBaggio Jan 3 '18 at 17:44
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    $\begingroup$ You don't really need guided missiles when you have point and click instant death rays. Early planes are not going to dodge anything. Also airships are incredibly large targets without any real way to defend themselves. The only disadvantage of using PGM would be that it would be a waste of Mars money. $\endgroup$ – A. C. A. C. Jan 3 '18 at 18:56
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    $\begingroup$ @A.C.A.C. My reason for saying that they have need of weapons other than the heat rays is broader than air defense. For one, they are incapable of indirect fire or over-the-horizon attacks, and secondly they are less reliable in precipitation and fog. They seem also to be relatively close ranged weapons even in suitable environmental conditions. $\endgroup$ – Mike DiBaggio Jan 3 '18 at 21:54
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Wood aircraft are not necessarily stealthy. They still contain a fair amount of metal, in the engine, and wing bracing. RCS is not just how much metal, it's the shape of the metal, as radar cross section is how well the target reflects RF energy back to the receiver. Wing bracing wires make great antennas to reflect radar.

Consider the case of a later aircraft, the Horten/Gotha 229, a flying wing with an airframe largely made of wood. It was long rumored to be stealthy, and Reimar Horten claimed that he had used a charcoal paint to cut the radar reflection, but the Smithsonian, who has the only known example of a 229, could find no evidence of the charcoal paint, and contemporary tests on a full sized model showed that the 229 had a radar cross section about 40% to 50% of a ME109, smaller but definitely not stealthy. It was the metal in the 229's engines and cockpit that reflected the radar.

Modern heat seeking missiles can pick out a fairly small heat source, especially if the sky is the background. A lot of ground attack aircraft and helicopters, such as the A10 or Apache, use shielding to mask the heat signature from shoulder fired heat seekers, so those missiles have been updated accordingly. Presumably, an invader would have such tech.

Actually, the greatest damage done to London during WW1 wasn't from the airships. It was from the early heavy bombers, specifically the Gotha G4 and G5, that Germany used in 1917, after the British figured out how to shoot down airships. The Germans discontinued airships as bombing platforms quickly, when they started losing a lot of them, while the Gotha's were as fast as the best fighter planes, and quite difficult to catch in flight.

I would tend to think that a technically advanced invader wouldn't use missiles against the rather fragile and slow WW1 vintage aircraft. They'd use something more economical, like a rail gun or directed energy weapon. Considering the numbers of aircraft they'd have to deal with, a rail gun with 200 slugs takes up a lot less room than 200 missiles.

Then again, a more advanced invader might not need to engage in direct combat against WW1 vintage weapons. They could target the country's leadership, tossing it into disarray, or its industrial infrastructure such as gas and electricity, putting its economy into a tailspin, things WW1 armies didn't have the capability to pull off.

Or, an advanced invader might decide to ally itself with one faction, say Germany as the more warlike, erode the British and French military, and let the Germans subjugate the rest of humanity with their assistance.

How could humanity win against that? Perhaps someone in the German military, realizing the implications of such an alliance (when would the invaders turn on the Germans?) could use the association with the invaders to learn their weak points, and communicate that to the rest of the world.

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  • $\begingroup$ It was a tough call to select best answer, but I picked this one because it addressed the radar cross section of wooden airframes in a concrete way. Cheers! $\endgroup$ – Mike DiBaggio Jan 7 '18 at 7:06
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I would contend that the effectiveness of PGM against slower-moving targets would depend on the type of guidance system, but only in the range of "effective" to "extremely effective". Purely-automatic systems might not see enough return for accurate targeting and subsequent - but those only came into being because manual/line-of-sight systems couldn't track faster-moving targets. We have the opposite problem here.

If your Martians are too advanced to use manual or semi-manual target tracking (possible, but we still use those types of systems when firing at ground targets from fast-moving aircraft), I'd say that the Martians could likely resort to using weapons designed for ground craft or even stationary targets. A modern medium-range air-to-air missile has a flight speed of over 3,000mph - in comparison, the paltry 120mph of the Fokker D.VII may as well be stationary. With those speed differentials, you could even fire the PGMs without guidance, line-of-sight, and hit most of the time. At the effective range of the Fokker's guns, you'd have little over 1s to react to an incoming missile.

And if the guidance systems just aren't doing it for air-to-air combat, just wait until the comparatively-limited-range WWI-era planes have to land, then light them all up at once.

Edits for clarity: There are many different types of "guided" munitions, with different levels of sophistication. Systems termed "purely-automatic" above would be the most advanced of these, sometimes termed "fire-and-forget". In these systems, the target can be identified either by the user or, in some cases, the munition itself. The target is then tracked by computer and the missile automatically guided to the target.

Less-advanced systems might have manual target tracking (beam-riding systems, e.g.) with automated guidance, automated target tracking with manual guidance, or fully-manual tracking and guidance.

Source

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    $\begingroup$ " With those speed differentials, you could even fire the PGMs without guidance, line-of-sight, and hit most of the time. " It's worth noting that a missile usually takes some time to reach maximum speed. I suspect a Fokker might fare better than suggest if in such naive scenario. $\endgroup$ – NPSF3000 Jan 3 '18 at 21:41
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    $\begingroup$ While it would take a missile some time to reach Mach 4, point-defense-type missiles are generally designed to target, close on, and destroy much faster-moving aircraft than a Fokker in relatively short order. They might have a few seconds to evade, but they may not be able to evade enough in the time the missile takes to get there. $\endgroup$ – Chris M. Jan 3 '18 at 22:17
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    $\begingroup$ No, missiles without guidance are unsuited to shoot down flying targets. Guided anti-aircraft missiles are not only guided to compensate for target movement, but also to compensate for small inaccuracies in targeting. There was an incident when over 200 unguided missiles couldn't shoot down a runaway target drone. And that was an aircraft which was not maneuvering intentionally to make targeting difficult. $\endgroup$ – vsz Jan 4 '18 at 7:12
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    $\begingroup$ "Purely-automatic systems might not see enough return for accurate targeting" even a 'cheap' FLIR camera will see a huge hotspot of any engine that would be in use on an aircraft. Doubtless current military hardware is better, and space-faring alien invaders would have even better technology. I can't see this being an argument. $\endgroup$ – Baldrickk Jan 4 '18 at 13:19
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    $\begingroup$ @Baldrickk That was actually the OP's argument/line of thought. I didn't want to dismiss it as impossible (although I agree with you), but rather to say that even if IR targeting didn't work against the smaller, cooler engines of turn-of-the-century aircraft, they stand little hope against anti-air systems developed even 50 years later. $\endgroup$ – Chris M. Jan 4 '18 at 13:29
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Stunningly well. Astoundingly well.. Hideously well...

The descriptions of the flying machines are, from memory, very scant, but we can assume that both from Well’s descriptions of Martian technology and the fact that the Martians could fly between worlds that they can fly faster, higher and with more maneuverability than even the best WW1 planes. While the radar cross section of a plane might not be big, it certainly would be enough for Martian sensors (they could identify military hardware on the surface of the Earth from mars) to pick up on.

Given that WW1 planes were primarily made of wood and the Martian ships were made of metal it’s possible that a Martian missile could destroy a plane without even detonating. There are accounts of RPG’s passing straight through the hulls of cargo planes without detonating on account of the relative thinness of the hull, and unlike modern cargo planes WW1 planes can’t deal with having meter wide holes punched through them. Of course, if the bomb does detonate the plane will pretty much cease to exist anyway, so..

On the subject of airships: the Martians, having slowly but surely drawn their plans, would likely fit incendiary payloads.

Whoomph.

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    $\begingroup$ I think it's an open question whether the Martians made a controlled flight or were launched ballistically. IMO, the descriptions from the book sound more like they were launched out of cannons or mass drivers or something, and the cylinders did not seem to make a controlled landing. Also, it took several days to weeks for them to assemble the first flying machine (not sure on the exact timeline at the moment, but it was definitely not ready during the initial stages of the invasion). $\endgroup$ – Mike DiBaggio Jan 3 '18 at 18:38
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    $\begingroup$ @MikeDibaggio: Regardless of method of transit, they had enough tech to make a controlled atmospheric re-entry that didn’t immediately turn the occupants to mush. That speaks of incredibly sophisticated aerodynamic understanding and propulsion technology. $\endgroup$ – Joe Bloggs Jan 3 '18 at 18:41
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    $\begingroup$ @JoeBloggs I'm more impressed that the occupants weren't turned into mush on launch, if they were launched by a mass driver... $\endgroup$ – John Dvorak Jan 3 '18 at 19:11
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    $\begingroup$ If the planes are made out of wood, I wonder if incendiary ammo would be a better choice than simply running a metal rod through the chassis. $\endgroup$ – John Dvorak Jan 3 '18 at 19:38
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    $\begingroup$ After the destruction of the Thunderchild, the narrator of "The War of the Worlds" sees a Martian flying machine as twilight descends. This is only mentioned once and never appears to influence anything else the Martians do, but is is canonical that the Martians have heavier than air flight. $\endgroup$ – Thucydides Jan 3 '18 at 21:59
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I'm not really clear why you think the Martians don't have "tactical" flexibility given they are equipped with the equivalent of nuclear powered megawatt infrared lasers and wide acting chemical agents mounted on fast moving tripod war machines.

TV Tropes interlude:

Frickin' Laser Beams: The "Heat Ray" is a much more realistic description of the effect of a laser than most fiction has managed since lasers were actually invented. The "Heat Ray" as being invisible, making it terrifying as the protagonists can't see the beam, only what it's currently igniting. A high-powered (and by that, we mean nuclear) infrared-spectrum laser weapon would behave pretty much exactly as described.

The only conceivable Earthly weapons system which could engage for short periods of time would be ironclad warships (think of the "Thunderchild"), since the metal could absorb the damage from a laser weapon for a short time, the ship is compartmentalized enough to limit the effects of "black smoke" and it is also a mobile gun platform. Full fledged battleships or armoured cruisers would seem to have more of a chance against a Martian than a torpedo ram, the main issue is the ships gunnery would only extend inland so far, while the Martians would not be able to extend their reach beyond a short distance from the shore, so you clearly have a stalemate.

enter image description here

Typical period Armoured Cruiser

The Martians can obviously deal death and destruction to anything in line of sight using the heat ray (and that includes aircraft, even modern 4th generation jet fighters), and use black smoke to root out anyone attempting to hide under cover. PGMs are simply not necessary for the Martians to fight Humans.

OTOH, the reason the Humans got curb stomped by the Martians in TWOTW is because they were unable to hit the fast moving tripods. In effect, the force that needs PGMs to leverage the limited amount of firepower they have is the Humans!

Now while Steampunk or Clockpunk PGMs are difficult to arrange, one could imagine a large glide bomb like weapon launched from a sufficiently high flying airship or airplane (or perhaps catapulted from a warship) that could achieve something of this effect. Discounting the idea of a Kamikaze pilot, the device would likely resemble the Japanese Yokosuka MXY7 Ohka or the German Fieseler Fi 103R Reichenberg

enter image description here

Ohka

enter image description here

Fi 103

Oddly enough, even in a Steampunk world there are solid fuel rockets, and the idea of a pulse jet is simple enough that it possibly could be developed under the emergency circumstances of a Martian invasion. A form of turbojet was invented and flown in 1911 (using a conventional IC motor to drive the compressor), so jet engines are also possible.

Using a ground or air observer, the weapon would be guided using a variation of the SACLOS (Semi Automatic Control Line Of Sight) mechanism that TOW missile uses. A bright flare on the back of the weapon is used as the reference, and the observer uses a sight to line up the missile and the target. If the missile drifts away from the target (or the target moves), the observer uses a heliograph to send a light signal to the receiver mounted on the back of the missile, which then activates a clockwork or other mechanism to move the control surfaces to correct the missile's flight. A ground observer could be used to guide a low flying version of the missile catapulted from a warship, giving the Royal Marines some glorious opportunities to win the VC.

The obvious downside to this is the observer and firing aircraft are both very vulnerable during the flight of the weapon, so the SOP is likely several aircraft fire a volley of missiles at once to try to overwhelm the tripod before it can shoot all the aircraft or missiles down. The race will to be building large numbers of missiles and launch platforms faster than the Martians can destroy them.

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  • $\begingroup$ Pusejets are simple enough to have been built from scrap by amateurs in a short time frame. (see a number of episodes of scrapheap challenge). They are about as simple an engine as possible. As long as suitable fuel, a pump and a metal tube can be produced, you can make a pulsejet. $\endgroup$ – Baldrickk Jan 4 '18 at 13:35
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    $\begingroup$ Better still for the OP, pulsejets were invented in Russia in 1864, although working ones were not built until 1906. $\endgroup$ – Thucydides Jan 4 '18 at 20:29
  • $\begingroup$ Thanks for the ideas on early human PGMs. They are valuable. WRT tactical flexibility, I explained that in a comment on the question. DEWs cannot fire indirectly and, even going strictly on the book's portrayal, they are restricted to relatively close range, and at longer ranges the Martians prefer to use the gas canisters. DEWs are also degraded by bad weather and, as I suppose in-universe, they're quite fragile in the field. Chemical weapons are tricky to control and the Martians themselves are vulnerable to them (hence the use of the steam cannons to 'clean up'). $\endgroup$ – Mike DiBaggio Jan 7 '18 at 6:53
  • $\begingroup$ Tactics means the way you move, shoot and communicate to deliver effects to the enemy in contact, and Martians in the book have few restrictions on that. PGM's leverage limited firepower and resources, so in tactical terms it means a smaller force can deliver the same punch, or needs less ammunition for the desired effect. Since the Martians can move rapidly to bring heat rays and black smoke to bear on targets (and heat rays have at least the same range as direct fire artillery), they can deal with targets in the open and under cover wherever they detect them. $\endgroup$ – Thucydides Jan 7 '18 at 14:00
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Away from line-of-sight, the humble WWI craft might prove difficult to detect. Here are some approaches that might be used by Martian invaders for fielding precision weapons against low-heat-signal, slow moving airborne targets:

Create larger, slower, more expensive missiles with more powerful sensors

This involves building an advanced, missile-mounted antique plane detection system. The martians would have to producing enough of them to field, attach them to missiles, and sacrifice them upon detonation, expending components and rare materials. Such systems probably rely on tracking engine noise, or high visibility of the Fokker in daylight. Strategies to defeat this would include flying at night-time, or switching the engine off to glide. Such a scenario would result in cat-and-mouse games, as the Martians listen for buzzing WWI bombers at night-time, hesitating to fire off their expensive missiles.

Invest in reconnaissance platforms

One high-altitude reconnaissance craft can guide several missiles. The missiles themselves can be very inexpensive, containing only propellant, steering and communications equipment. A potential drawback of this approach, in a planetary invasion scenario, would be high network load (hundreds of missiles flying at once). This might be exploited by Earthly defenders, who would employ swarm tactics to overwhelm the reconnaissance system. Fortunately, Earth planes of the WWI period fly very slowly, decreasing the need for Martian missiles to consume tracking data. The slow speed would help the Martian missiles keep on target, even with network overloading issues.

This tactic would make the reconnaissance equipment itself a target. Battles would be fought to keep the "eye in the sky" open.

Increase the missile blast radius

World War 2 anti-aircraft rounds had a blast radius of about 100 metres. The goal was merely to project shrapnel (flak) into the air and let the enemy planes fly through it. Given their expertise in high-energy thermal devices, Martians could increase the effective range of a single detonation to at least a mile. Flying at 120 mph, and with fore-knowledge that they are about to be targeted by a single round, a Fokker would have about 30 seconds to get out of range. If large-radius anti-aircraft rounds are as inexpensive to the Martians as WWII munitions were to humans, they could potentially be used in a barrage, making large areas lethal for aircraft to fly in.

Potentially, such barrages could even be guided from observation bases located on Mars itself. Using a little trajectory prediction, aided by the limited top speed of the Fokker, the Martians could likely hit their targets even with a 6 min (closest Earth-Mars round-trip time) delay for tracking.

Ignore the planes until they come into line-of-site

WWI weaponry had limited range. Approaching close enough to cause any damage, even to Martian assets with minimal defensive weapons, would likely be suicide.

One possibility is for human defenders to retrofit purloined Martian weapons onto their planes. However, this would be limited by the low carrying capacity of WWI planes. High-energy weapons tend to be very bulky (size and weight are apparently the main obstacles for DARPA's laser systems) or generate a lot of waste heat, so fielding airborne offensive platforms in meaningful numbers would likely remain impossible for Earth's defenders.

Thus, zapping humans defenders as they appear might, in itself, be a most effective Martians offensive tactic.

(This last point isn't exactly an answer to the original post, just a note that precision-guided weapons might not be necessary.)

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If the Martians have the equivalent of modern anti-aircraft missiles they very well might not work--the slow-moving early aircraft would look an awful lot like decoys because they're not moving fast enough to be a real target.

However, the Martians don't need them. If they have stuff like modern missiles they also should have stuff like modern point defenses. A Phalanx cannon would eat any WWI aircraft and spit out kindling before it closed to attack range.

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To directly answer your question they would be very effective. However you may need to look a few steps further from the battle to the war. Humans could cheaply and easily mass produce balloons, airships and simple planes. Assuming a one-bomb one aircraft ratio, would the attackers be able to produce enough guided missiles to cope? If they do not have the capability to manufacture the weapons then they would have to rely in a fixed and dwindling supply. I suspect that the martians would either run out of weapons or else have to develop combat aircraft or some form of reusable weapon like a stand-off missile or a drone gun platform.

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An unforeseen issue may be reliably detonating a missile on hitting an aircraft made of too light materials. If the weapon is detonate on impact there is a fair chance it will simply punch a hole through light wood / canvas without a warhead being activated.

On the other hand modern tracking missiles are designed to explode next to the target and project shrapnel into it which would still work fine in this scenario.

This method tends to be more effective at killing the pilot and prevents the other end of this problem, where the trigger is broken in the impact on hard metal without detonating.

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You could avoid radar and go for kinetic kill by having the Martians build piloted armored aircraft that simply fly through anything which opposes them, no guns or explosives required. Although a ram on the nose of the aircraft might not work so well, a weight suspended by a strong wire would probably be able to do pretty massive damage to anything the humans could put up. Obviously, humans don't build fighter jets this way because guns and missiles. But if Martians are simply going for the dumbest, most reliable way to gain air superiority, the humans of your era have nothing to shoot down or defend against supersonic aircraft that can cut them in half while deflecting the occasional lucky shot from a WW I-era machine gun.

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