If Nazi Germany were to develop a dieselpunk version of a Zaku I using 1939-era technology, what would their name for a mobile suit be?
I was thinking that sometime in the thirties, the highest echelons of Nazis are discussing Jewish Physics when one of them brings up the Jewish legend of the golem (know thy enemy and all) as a dismissive example that fairy tale levels of stupid shit is the best those entartet untermenschen can possibly come up with. Except Hitler, being Hitler, promptly starts handing out orders that military R&D is to round up the top mechanical engineers of the Reich and have them top that with something Aryan that would strike terror into the hearts of the enemy and scare them away from attacking the Fatherland ever again.
Not to mention that the whole idea of a giant killbot is so ridiculous that western intelligence efforts will never ever believe it.
Development is difficult and ponderous. The first major issue is found to be the powerplant: even with batteries borrowed from the Kriegsmarine's Type VII submarine, the prototypes couldn't operate for more than a few hours while untethered and nuclear reactors haven't even reached the conceptual stage yet. Ultimately, the engineers just threw up their hands and supplemented the battery with a diesel generator.
Then there was the fact that not only the whole thing was so insanely mechanically complex that no human could possible drive and fight at the same time, it was hard enough just to learn how to make it walk without losing balance. Ultimately, a three-seater cockpit was squeezed in: a driver seat at the bottom with levers and pedals for operating the leg hydraulics; a gunner seat in the middle with foot pedals for rotating the torso, hand-operated winches for moving the arms and a small cathode ray tube TV screen connected to a boresight camera mounted onto the bottom of the hand armament; and finally a commander seat at the top with pedals for rotating the head so that it can be used as a periscope with a far longer line of sight than any tank's.
Even so, it was an utter nightmare to maintain, even with compromises put into the design. The arms had a highly limited range of motion to keep the joints as robust as possible. The fingers weren't actually usable, nor did the hand armaments mount an external trigger; those handles were just handles for holding and aiming the weapon, with the firing mechanism being directly wired to the gunner's controls. Switching weapons mid-battle is also out of the question.
Nevertheless, the go-ahead was given for a limited production run. And thus in September 1939, the Polish Army received the fright of their life...
Although ponderously slow and cumbersome, absolutely nothing the Polish had on hand could go past the Sd.Kfz.400 Gehenpanzer I's massive armor plates. Even artillery shells bounced right off before either the head-mounted 2 cm autocannon or the magazine-fed semi-automatic rifle version of a Flak 38 obliterated the offender. Far too slow to participate in blitzkrieg maneuvers, the behemoths were instead driven straight into the heaviest clusters of enemy resistance like a hammer while the conventional forces followed behind to provide covering fire against flanking attempts and to mop up any resistance left after the big boys' passing. Not that the latter was really needed; brave as the Polish were, more than once the Germans had the tattered remains of whatever Polish unit they most recently encountered hysterically begging to surrender after the Gehenpanzers were through with them.
To them, the Gehenpanzer was not a monster of a war machine; to them, it was an act of God. As hodgepodge the design was, its sheer psychological effect who'd never seen anything like it in fiction, much less in real life, was undeniable. Think Tiger tank times 10.
In the spring of 1940, the Wehrmacht rolled into Denmark while the Gehenpanzers remained home to receive a thorough check-over and tweaking in preparation for the real deal in France. Hitler personally inspected the war machines during this downtime and upon returning to Berlin, immediately approved a budget expansion for expanded production and crew training. Meanwhile British and French intelligence were scratching their heads in confusion about what could've happened in Poland because the first-hand accounts they have speak of invincible steel giants that wield cannons like men wield rifles. They speculate it may have been just a really big tank that spooked the refugees, or maybe even a Guntank-esque deal. But walking machines? Preposterous.
Mechs are powerful, yes, but still reliant on combined arms warfare to be effective due to their slow walking speed. They do not replace tanks or anything; in fact, late-war tanks like the IS-2 can take down a mech just fine. Additionally, the Gehenpanzer I Ausf.A that first saw action in Poland and France lacks proper environmental shielding for subarctic and desert conditions, which is why the Germans still couldn't roll over Russia (they managed to close the Persian Corridor and claim the Caucasus oil fields, but their supply lines were too overextended to go any further and even though they actually reached Moscow, it became this timeline's Battle of Stalingrad due to the Gehenpanzers having trouble with their hydraulics freezing up). The Ausf.B that was developed based on Rommel's input pipes the engine coolant through the armor plates to heat/cool as needed, so it can run marginally better in harsher environments. Mountainous terrain is also a problem (which is why German mech troops didn't participate at Dunkirk: they couldn't get the mechs through the Ardennes in a reasonable timeframe, so they threw them at the Maginot line as a distraction while the rest of the Blitzkrieg took the northern route).
As for the other nations in the war, they naturally tried to replicate the design, but it took years. In the USSR, Stalin immediately gave the order as soon as the Germans bragged about their newest toy during the Paris victory march, but it doesn't actually bear fruit until early 1945 and Stalin himself was severely injured in an assassination attempt by Skorzeny and co. while personally inspecting the research effort (as motivation for the engineers after their predecessors were shot as saboteurs due to having failed to deliver results as swiftly as Stalin would've liked). In the west, the US got their hands on disabled German mechs captured in Africa and eventually reverse-engineered them into a design of their own; the British were already hamstrung with resources due to shit going down in the Atlantic, so they let the US do the manufacturing and only pitched in with R&D. The US only deployed mechs in Europe; for the Pacific front, it was simply too much hassle to keep shipping the things from island to island without being able to deploy them from assault ships to support landing operations (too much weight and not enough displacement to float and not watertight enough to walk to shore on the seafloor). For the same reason, the Japanese never bothered with the concept themselves until decades after the war when they've taken notes from the US mech troops stationed at Okinawa.
Where the development timeline goes from there, I'm still not sure. What I'm thinking of:
- First-gen mechs saw service in Korea, with some improvements. The US brought their mechs with them; China didn't have the tech yet, but the peninsula's mountainous terrain worked in their favor to some extent (hilly terrain generally favors mechs due to being able to terrain-mask their legs, but their feet do not have enough traction to traverse very steep slopes the way tank treads could).
- Second-gen was in service by Vietnam. All-around better mobility, started using composite armor. Very limited ability to swap hand-carried weapons during battle.
- Third-gen was developed in the 1970s. Switched from diesel to nuclear, which solved the limited operational time issue but resulted in numerous accidents; early third-gen models are generally considered Armored Coffins by their crews. First automation features appear at this time, though still very rudimentary. Preliminary experiments into hover propulsion for faster movement, eventually shelved because contemporary technology wasn't advanced enough to make it work.
- Fourth-gen was developed in the late eighties, seen action in the Gulf War. Started using computers and electronic fire control. Joints reinforced with reactive armor. Now has fully animate hands, although they're still awkward to use.
- Fifth-gen begins to appear in the early 2000s. Fully computerized, although still not to the part where one person can drive it. Hands properly work now. Preliminary experiments into shelving the nuclear generator for hydrogen fuel cells.
- Sixth gen... no idea. US wanted to equip theirs with railguns, but couldn't get the tech working in time. Hardkill active protection systems are a thing.