Fuel for Thought: How Hearts of Iron 4 mirrors the tactical & strategic impact of fuel on warfare

By Jack Trumbull 25 Mar 2019 0

Hearts of Iron 4’s huge new expansion, Man the Guns, was released at the end of February, and we have been very excited about its release. One of the most anticipated features that came with Ironclad, the update that launched with Man the Guns, was the addition of fuel. Now, the thinking was, players would have to think more strategically in their conquests because their vehicles need that fuel in order to operate. In practice, fuel does add a significant layer of strategic thinking to the game, but it falls short of being an entirely accurate and engaging reflection of fuel’s use and importance during World War 2.


Before we dive into how fuel works in HOI4, it’s important to understand the historical importance of fuel to the fighting forces of World War 2. This was the first major conflict that the need to supply large amounts of vehicles appeared, and several armies at the outbreak did not have a sufficient logistical doctrine for the handling of supplying those vehicles. Troop movement during campaigns frequently utilized trucks, half-tracks, and tanks, all of which needed to be supplied with fuel.

HOI4 Fuel Japan

The desperation for fuel drove some of the more critical campaigns of World War 2. The Japanese in 1940 and 1941 did not nearly produce enough fuel domestically in order to meet the needs of their army, navy, and air forces: a situation exacerbated by sanctions placed on them by the Allies and the United States. To continue their drive into China, the Japanese attacked the United States fleet at Pearl Harbor in an effort to stop the fleet from interfering with Japanese plans to capture crucial oil-producing islands in the South-Western Pacific. The Germans too gambled on an aggressive offensive in late 1944, when they attempted to seize Allied fuel depots in Belgium with the goal of keeping their fuel-starved tanks operating.

The need for fuel in the front line was not only felt by the Axis powers. One particularly famous example is that of United States General Patton’s push towards Germany in mid-1944. Patton’s army quickly overran German defensive positions, but stalled as they ran out of fuel for their tanks. Fuel that could have been directed to Patton’s forces was spread out to maintain a wider logistical coverage of the whole theater, and the retreating German forces were able to re-establish a defensive line.

US Fuel Mexico


So, how is this reflected in HOI4’s newest update? Firstly, oil is no longer used in the production of vehicles, making its sole purpose to create fuel for the war machines of the world. This is done automatically, with each unit of oil in a given territory (perhaps representing individual drilling areas) being converted into fuel. The amount of fuel gained can be increased by research and building refineries, and the processed fuel is placed into constructed fuel silos, where the national fuel stockpile is kept until needed by vehicles.

Practically, this forces the player to keep an eye on their fuel gauge, particularly when setting up naval forces. Ships are by far the largest gas-guzzlers in HOI4, with a capital ship using about as much fuel per hour as 5-10 average tank divisions. This meshes well with the new naval combat system, where fleets are split into smaller task forces, ideally meant to have light ships patrolling for enemy fleets while the capital ships sit idle in port, not consuming any fuel until needed for a decisive battle.

For a state which depends on their navy, fuel becomes one of the most important resources to secure early on in order to ensure dominance, particularly so in the case of Japan. Japan, as mentioned before, were extremely reliant on external shipments of fuel in order to keep their operations rolling smoothly. It’s with Japan that the fuel system truly shines, as they’re made to make tough choices between maintaining a dominant navy or shifting more resources to supporting their army with armored vehicles. Alternatively, Japan can repeat history and grab the oil-rich Dutch colonies in the South-Western Pacific in an effort to not have to make that difficult decision.

HOI4 Fuel US

However, the fuel system in other states can easily feel like any other resource. Oil can be acquired through trade, in exchange for civilian factories, and fuel can be sent as a lend-lease item, meaning that states can build up a healthy stockpile before the war begins. States that have oil naturally might never need to worry about having enough, as is the case with the Netherlands, Mexico, and especially the United States. The United States is such a powerful force with the new fuel system that any faction that is able to maintain good trade relations with them (and doesn’t have all their convoys carrying the oil sunk) can be assured of essentially endless fuel reserves due to the United States’ ability to have over 1500 units of oil extracted at a time.

In wartime, a particularly lucky player may come across a fuel silo in enemy territory. Doing so will grant that fuel to the capturing player. This seems like a feature that could be used to determine offensives just as naval bases, major cities, and airfields are deciding factors in the location of an assault, but curiously, fuel silos don’t appear on the map for enemy players. All a player can learn about enemy territory is decided by how much “intel” they have on the province, but that will generally only show that there are a minimum of x number of factories. For something as important as the location of fuel stockpiles, it’s bizarre that there’s no indicator of the presence of fuel silos in a province, especially when there was at least one noted offensive during the war that was partially motivated by the hope of capturing fuel.

Once a state has the fuel it needs, it’s sent to the front in a similar fashion to general supplies. If a territory has poor infrastructure, the fuel-seeking units may run dry if they are constantly operating, and will have to wait for the fuel to “catch up” to the forward units. This is a nice touch that can give the feeling of over-extending a supply line during an aggressive attack, but it is difficult to delegate fuel to the needed forces when fuel is tight. It would be very handy if there was an option for an army to get preferred access to fuel (it’s unclear whether changing the reinforcement priority for a theater affects the order or amount in which units get refueled), or to have the spearhead battle plan automatically grant preferred fuel access to simulate a proper Blitz. Regardless of ways to improve the system in the future, as it is now, fuel seems to be either an “off or on” switch.

HOI 4 Fuel Japan 2


While it was not a set goal of Man the Guns/Ironclad to do so, fuel has made 20th century colonization a recurring theme in new campaigns in HOI4. For both major powers like Germany and Japan, as well as smaller states such as Greece and Turkey, maintaining a solid supply of fuel is necessary to at least have air support for ground forces. Most states aren’t capable of producing the amount of oil that would be needed during wartime, and frequently turn to declaring war on their oil producing counterparts to quickly build a stockpile.

Earlier versions of HOI4 included some amount of imperialist resource grabbing, but gaining access to fuel become one of the most important considerations for players in the early game. Axis players or other fascist states can reasonably expect democratic powers to refuse to trade them fuel even before a conflict, so seizing oil rich land in South America or the Middle East becomes a common practice. Post-war, assuming there are two major factions left standing, taking these states could also be an exercise in denying those sources to the enemy faction. This results in a surprisingly realistic reflection of the post-war period, with intervention in oil producing states very common from both the Communist-aligned states and NATO. With this behavior relatively common in HOI4, it seems like there’s reasonable groundwork for a future Cold War-based game as factions seek to assert dominance over unaligned but strategic states.

HOI 4 Fuel Globe


Fuel is now an unavoidable part of HOI4, but it can be confusing to wrap your head around, especially as a state with scant natural oil sources. In order to be able to produce fuel without relying on foreign powers, researching the refineries in the industry tab becomes key for aggressive states, or those that will be cut off by enemy blockades. These take up valuable building tiles in your provinces, but may be needed to at least fuel an air force, to ensure the enemy does not have complete dominance of the skies. Furthermore, building additional fuel silos early on can help offset a fuel source being cut off later on; if you have millions of gallons of fuel sitting around, you won’t need to worry about producing more for years (unless you have a very big navy or mechanized army, then you might still need to worry).

In terms of building land forces that use fuel, it’s important to remember that every different vehicle uses a different amount of fuel per day. An infantry division that rides around on trucks may have less armor than their counterparts in halftracks, but the former will use less fuel. Similarly, heavier and more advanced tanks will use more fuel, so it may be worth it to stick with older, lighter models and use army experience to make them more useful. Worth mentioning as well is that infantry divisions that require trucks for towing artillery and other support guns around strangely don’t consume any fuel, so there’s no need to worry about supplying them.

HOI 4 Fuel Units

When composing your forces, most states should have several “leg infantry only” divisions that don’t use fuel. Divisions that need fuel should be used in concentrated areas like a scalpel when fuel is running low. Remember, there’s no option to “go easy” on the refueling for units, so any time they move or fight, they will be using up valuable fuel. States with a fuel deficit will need to keep track of these forces and use them to push through enemy lines at strategic locations, before moving them to another area of the line and repeating the process. These armies will ideally have large stacks of infantry manning the defenses, supplemented by the armored/mechanized/motorized divisions pushing forward in their area. By operating in this manner, you can make your fuel usage more efficient while still retaining the extra firepower and mobility of mobile divisions.


Fuel has certainly increased the strategic thought necessary to play Hearts of Iron 4. Players now need to think several years in advance in terms of fuel, rather than worrying only about immediate needs being filled in terms of other resources. This rush for fuel has (perhaps unintentionally) caused players to think as imperialists in order to maintain access to fuel, simulating the exploitation of these states that was common in the early-mid 20th century. But even though fuel has established a more familiar historical narrative, the tactical use of fuel remains basic as of Ironclad 1.6.1. Hopefully the fuel mechanic will get better with time and further support.



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