In my world, which is partially based on a WW2-style environment, there are two large countries, namely A and B, that are fighting each other.
A is a Nazi Germany-type country with fine revised tactics, like the blitzkrieg, i.e. entering territory so fast, that the enemy doesn't even have time to react. A also has superior technology, like long-range supersonic bombers and heavy-duty tanks that can ravage even through muddy terrain and all sorts of weather.
B, on the other hand, is a Soviet-style (remove the communism part) country, with a ton of personnel but, due to purges of military generals etc., the army is so badly led, that even with tons of soldiers they are agonizingly slow, such that even with good ammunitions and stuff, a smaller but better led army would be able to defeat them.
A and B are fighting each other in a bitter war to acquire control of uranium fields in the black-encircled region given in the map below (credits to Inkarnate):
This map is the entire map of the world, and, since my world is about as big as Earth, you can use a 1:100,000,000 scale.
However, we run into a problem.
A is blockaded and sanctioned from obtaining oil to fuel its war with B. Meaning that alongside B, there are other countries that are indirectly in the war, by blockading A from getting oil, such as C and D, on the western portion of the map. B, C and D form an alliance group that is analogous to what would be the Allied forces in WW2.
E, the island at the west of the map, was the area that A procured oil from. But as C and D have blockaded it, A has resorted to getting oil from within its territory only, which only meets about 15% of its fuel demand.
I see a congruity between the story in my setting, and World War 2. Just like the story in my setting, Nazi Germany could have theoretically defeated the Soviet Union during Operation Barbarossa due to better technology, aerial superiority, etc. However, Nazi Germany lost the war due to oil. Basically, most of the oil that Nazi Germany obtained was from Soviet Union (ignore that for now) and Mexico and the Caribbean (the analog for E in my setting). However, due to its close proximity to the USA (analog for C), Mexico had to stop its oil exports to Germany, which was disastrous for Operation Barbarossa, as the Wehrmacht and Luftwaffe were heavily reliant on petroleum to fuel their tanks, cars and fighter jets. This is an extremely massive reason why Germany lost the war
(and Austrian Painter and his bois got rekt).
My world's setting also faces this problem. Due to the blockading of E by C, D and B to prevent A from getting oil, A's tanks and supersonic long-range bombers are practically useless due to lack of oil to fuel them, as I mentioned before. A's domestic oil production is barely 15% of their demands. There is no way to get oil from E without declaring war on all three countries at once. And although A has a massive army, that is nothing compared to the full might of all three countries C, D and B. Which means that A now has to look for an alternative source of fuel, something that it can manufacture easily using domestic resources.
I have been told that Nazi Germany was contemplating synthesizing oil from coal, but in my setting, A cannot do that, as the process is extremely inefficient and wasteful of energy. Furthermore, A doesn't have a plethora of coal deposits, which means that the coal-synthesized oil scenario is impossible. (However, if these assumptions are incorrect, feel free to point it out and I will gladly edit my question.)
What is the easiest fuel a blockaded, sanctioned nation can procure/synthesize during a war?
- The fuel cannot be something whimsical or ridiculous. For example, something like "Antimatter Steam Engine" or "Muon Fusion Tanks" are totally out of the question.
- The fuel must be something that can be manufactured with 1980s technology.
- The fuel is something that is very easy and not very time-consuming to manufacture.
- No nuclear fusion/fission-based improbable tech. Uranium is terribly inefficient for vehicles, as most nuclear engines are basically steam engines, which means that a ton of water is required for powering, making a fission powered vehicle impossible—and don't get me started on fusion-powered vehicles.
- The fuel can either be synthetic or natural.
Some additional info:
My world's technology is comparable to that of the 1980s.
A has about 2.5 million troops, 4000 aircraft (mostly long-range supersonic bombers), 20,000 tanks and 15,000 submarines.
B, on the other hand has 7 million troops, 5000 aircraft, 40,000 tanks, but zero navy. Despite the massiveness of B's army, it is so badly led, that it can in theory easily be defeated by A.
C, D and E aren't directly involved in the war, except for the blockades and stuff, so the question of how much troops they have is irrelevant.
If people want an analogy of what the blockade looks like, try to imagine something like the British blockade of Germany during WW1.
Some clarification on the "uranium fields":
Uranium and nuclear fission are prevalent. In fact, the reason A is invading B is to wrest control of the uranium fields on the map. A does have nuclear fission tech; however, there is an acute shortage of uranium ore in A's territory. That is why A is invading B to get uranium. Try to think Nazi Germany invading Kazakhstan for uranium, if you want a real world analogy (which neither was planned nor succeeded, but makes for a clear analogy).
The "fuel", however, is not power generation or anything like that. The "fuel" that A needs is basically fuel to power vehicles, locomotives, tanks and planes. I am aware of the fact that uranium or anything remotely nuclear is a terrible choice for fuel as it is incredibly inefficient, and moreover, having a bunch of dirty bombs carrying radioactive fuel isn't particularly safe.
EDIT: I have often heard that the Fischer-Tropsch process was used by the Third Reich to synthesize fuel for its war machine during WW2. Although this scenario might seem plausible, it has been stressed in this question that Nation A does not possess a plethora of coal. And even with coal, the FT process is terribly inefficient, being at best, only meeting barely 10% of the war demand.