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HoI4 Dev Diary - Subs and Convoy Raiding

Greetings, I am a game designer new to the HoI4 team. This is my first dev diary, so be gentle ;). Also, sorry for the late post today. I am an American and when it comes to WW2, we show up late.

Today’s diary entry covers our improvements to submarine convoy raiding. In past versions of HoI4, submarines have not really pulled their weight. We have sought to change that and make them worthwhile to build. I recently put these changes to the test by playing a Germany campaign.

My naval plan as Germany was to exploit the central Atlantic and Cap Verde Plain with a submarine wall. This would hopefully prevent England from getting necessary resources from the USA and the colonies. The biggest effect of this resource shortage would be the UK running out of fuel, crippling both their navy and air force. This would hopefully open the UK to sea lioning before the USA joins the war or at the very least, make winning the air war very easy and cause permanent damage to the UK’s fleet.

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We have previously mentioned the spotting system, and how naval task forces are revealed over time. This functions a little bit differently for subs. Spotting an enemy sub outside of combat is based upon chance. The chance for this to happen is based on how quickly the spotter will spot their target. However, it is possible for a submarine to have a large enough advantage in spotting that the submarine task force will not be able to be spotted. However, convoy escorts will still be able to fight against submarines once combat is initiated, even if subs are not normally detectable by enemy taskforces on the map.

This system creates a tech race between sub stealth and sub spotting, with subs having a better chance of getting an advantage in the early game. Previously, submarines would eventually be detected and killed no matter how good at hiding they were. This is no longer an inevitability.

Before beginning the war, I made sure to complete the German naval focus line down to “U-boat Effort.” Along with getting a research speed boost and some dockyards, the focus gives Germany access to a “Cruiser Submarine.” This sub is a sort of tech 2.5 Sub with extended range, some unique module options, including catapult planes, and the ability to be upgraded with a snorkel.

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Part of my plan for giving England a hard time included mining up the English Channel. I executed this plan with a cruiser sub equipped with naval mines and plane catapults. These plane catapults boost the sub’s surface detection, giving them an advantage in being detected and helping them remain invisible, at least for the first couple years of the war.

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I made a tech 3 sub-variant for minelaying the Eastern North Sea and a tech 3 raider-sub for Cap Verde Plain. When I demanded Danzig from Poland in August of ‘39 I had 79 Subs of various roles ready and much of the Trade Interdiction doctrine complete. This focus on raiding will give my subs a further detection advantage over other countries that have yet to complete their convoy escort doctrines.

Speaking of the naval doctrines, we have made some changes all around to account for the new combat system and apply a bit of balance. In particular, we have given some buffs to the Trade Interdiction doctrine to make it more attractive than it was previously. We have added additional survivability for submarines and more of an edge in surface detection values. Capital ships have received some defensive increases as well.

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Torpedo reveal chance is a new thing for subs. When subs are in combat, attacking no longer guarantees that a sub will reveal itself. Baseline, subs have a 50% chance to reveal themselves when launching a torpedo volley. This can further be improved through doctrines and admiral traits. This makes ambushing protected convoys safer and retreating when too many destroyers show up easier.

In my campaign, I capitulated France in early December of ‘39. To help with the Axis’s naval situation I formed Vichy France. Before France fell they had been contesting my raiding of Cap Verde Plain to the best of their ability, but I was still seeing some success. Forming Vichy France put more ships in the hands of the Axis and would further help to stretch the limits of what England could endure at sea.

With Vichy France on my side, early 1940 saw a massive spike in convoys raided as Cap Verde Plain and the Mid-Atlantic were now completely covered. By this point, I had ~20 dockyards producing subs for minelaying and raiding. All of my newest tech 3 Raiders were seeing great success in under the guidance of Karl Dönitz. Even when contested by British convoy escorts, they were able to get a respectable amount of kills and retreat. Naval bombers were also ramping up operations in the English channel.

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We have added a new effect to convoy raiding, war support reduction due to raiding. By mid-1940, Canada had been raided to 0 convoys and had their war support reduced to a point where they were no longer able to support War Economy. This helps to promote raiding and discourages blunt forcing convoys through an area where you are being raided.

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By early ‘41 the UK had been choked out of convoys and fuel and was unable to keep their navy running and were about open to a naval invasion. By mid ‘41 I had naval invaded the UK and was Setup for an attack on The USSR.

See you all next week!

Rejected Titles:
-Raiding and Reaving, 1940 edition
-Subs, they're not complete trash now!
-Under the sea, Darling its better
 
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Submarines need much more attention. They need more modules for deck guns and anti-air guns. They need more historically accurate engines, ranges, speeds, torpedo tubes and torpedoes. The ranges on the cruiser submarines are completely off. They should be three to four times higher. Snorkels and Radar should not be mutually exclusive that's ridiculous. Midget submarines which were produced in the thousands need to be added. Transport submarines which were produced in the hundreds should be added. The special Japanese huge I-400 Class et al need to be added. Along with their small number of aircraft which were not just scouting floatplanes. They planned on using these submarines and their planes to bomb the Panama Canal. They should be able to operate like normal aircraft. And it wasn't just the I-400 Class that had planes. Many others did as well.

A lot of work needs done on Subs.
 
Submarines need much more attention. They need more modules for deck guns and anti-air guns. They need more historically accurate engines, ranges, speeds, torpedo tubes and torpedoes. The ranges on the cruiser submarines are completely off. They should be three to four times higher. Snorkels and Radar should not be mutually exclusive that's ridiculous. Midget submarines which were produced in the thousands need to be added. Transport submarines which were produced in the hundreds should be added. The special Japanese huge I-400 Class et al need to be added. Along with their small number of aircraft which were not just scouting floatplanes. They planned on using these submarines and their planes to bomb the Panama Canal. They should be able to operate like normal aircraft. And it wasn't just the I-400 Class that had planes. Many others did as well.

A lot of work needs done on Subs.

No thread necromancy allowed bruh. This thread is like 10 months dead. The rules prohibit resurrecting any thread that has been dead for six months or more.

I don't disagree with you, but this definitely isn't the place for it.
 
The ranges on the cruiser submarines are completely off. They should be three to four times higher.

Keep in mind that 'nominal range' is very different to operational range. Nominal range is at most economic fuel consumption in perfect conditions with no hull fouling. None of these are true for a patrol of any duration (hull fouling builds up fairly quick, conditions very rarely stay (or at any stage are) perfect, and even if no attacks on convoys are made, subs may well increase speed, for less economical fuel consumption, to pursue a sighting report. Going from memory, the general rule of thumb for operational ranges (for all types of vessels, this may be a bit different for subs and, indeed, for particular sub models given where their engines are designed for maximum efficiency) is to divide the nominal range by 3 to 4.

They need more modules for deck guns and anti-air guns.

Subs don't engage in surface combat in HoI4. While this isn't accurate relative to history, subs also don't have a limit to the number of torpedoes they carry, so in an in-game sense it would never make sense to surface to preserve ammunition. You have a reasonable point with AA, although AA should also decrease sub stealth (all those pointy bits on the superstructure are not likely to help the subs' sonar signature).

Transport submarines which were produced in the hundreds should be added.

This feels like a bit of a stretch. In terms of submarines built as cargo submarines (or converted while under construction) and completed, I have (figures from Warship Vol 4 (Germany), Mussolini's Navy or Warships of the Imperial Japanese Navy, as appropriate):
  • German Type VIIF - 4
  • Italian Romolo class - 2
  • Japanese D1 type - 12
  • Japanese SS type - 10
  • Japanese Yu-1 type - 12
  • Japanese Yu-1001 type - 14
  • Japanese D1 type - 1
This gives a total of 55. You could also add in the I-505, converted by Japan, but that only takes it to 56. I haven't included the Japanese submersible barges, but given how unsuccessful these were, and that they usually made one-way trips that feels fair. Even then, I don't think they'd take the number completed to 'in the hundreds', but I don't have figures for them. The Japanese did plan to build them in the 100s (378 were planned for the Japanese types above, not counting the plans for the Yu-2001 type, that was never completed), but the Japanese had a lot of unrealistic plans, even when not taking into account the merchant shipping sunk or damage by strategic bombing, so would suggest interpreting these with caution. If I've missed any please let me know, am genuinely interested. I haven't included the long-range subs that were designed as raiding submarines first but then subsequently used as cargo submarines for long-distance trips between Japan and Germany, or to do supply runs to Malta (British subs) or Tripoli (Italian subs).

I'd argue the more appropriate point to argue would be whether (or whether not) subs (transport or otherwise) could be used for supply. I'd think it might be cool if they were, but they should be much, much, much less effective than a convoy. Given their limited effectiveness in supply operations (largely due to their very small cargo capacity, plus poor design for loading and unloading cargo), I don't think it's the end of the world that they're not in the game.

The special Japanese huge I-400 Class et al need to be added. Along with their small number of aircraft which were not just scouting floatplanes. They planned on using these submarines and their planes to bomb the Panama Canal. They should be able to operate like normal aircraft. And it wasn't just the I-400 Class that had planes. Many others did as well.

Like transport subs, while they were cool (and it would be cool if they were included), this would be a lot of work for an element that was strategically of tiny impact, whether talking actual (minor wildfires that burned themselves out) or prospective (12 I-400s making a strike with 36 single-engined aircraft) strategic impact.

No thread necromancy allowed bruh. This thread is like 10 months dead. The rules prohibit resurrecting any thread that has been dead for six months or more.

My understanding is that DD threads are exempt from this. We'll find out soon enough :).
 
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The game says range it doesn't say nominal range or anything like that. And according to Wikipedia the numbers are way off. And as I've discovered while trying to do a Pearl Harbor attack, my ships can't reach the target. This sucks. The historical ships cannot reach the target.

I saw on the Wiki that subs have 0.5 to 1.5 anti-air. But I don't know if that's still accurate. In any case, it should be its own slot on the ship designer. Some subs had impressive anti-air armament.

Here's are more Transport submarines. In the game I imagine them functioning as very stealthy convoys that can resupply isolated small island garrisons which is what they did in real life. They wouldn't be able to resupply vehicles though.

https://en.wikipedia.org/wiki/Type_3_submergence_transport_vehicle 38 and they planned to build 400.
https://en.wikipedia.org/wiki/I-351-class_submarine 1 and they planned 6.
https://en.wikipedia.org/wiki/Ha-101-class_submarine 10 and they planned 12.
And I'm sure there are many more.
 
The game says range it doesn't say nominal range or anything like that. And according to Wikipedia the numbers are way off. And as I've discovered while trying to do a Pearl Harbor attack, my ships can't reach the target. This sucks. The historical ships cannot reach the target.

Yes they can. Make sure you design your Carriers with Pacific designer + give them Battleship/Cruiser escort and they will have range.

Historically Pearl harbor was very much on the exact edge of the striking range of the Japanese and they required alot of refueling to pull it of. It's the same thing ingame.

Here's are more Transport submarines. In the game I imagine them functioning as very stealthy convoys that can resupply isolated small island garrisons which is what they did in real life. They wouldn't be able to resupply vehicles though.

As long as the submarines are given historical capacity I'm fine with allowing them to be build, but I don't see why anyone sane would ever want to build them... because they would have about 25 tons of cargo capacity compared to a single convoy ship capable of carrying 11000 ton = ~400 submarines have the same cargo capacity as a single liberty ship.
 
The game says range it doesn't say nominal range or anything like that. And according to Wikipedia the numbers are way off. And as I've discovered while trying to do a Pearl Harbor attack, my ships can't reach the target. This sucks. The historical ships cannot reach the target.

As Alex explained, it is possible (I've done it a few times as well), and it's almost spot-on in terms of the actual distance that the ships can travel in-game, versus what they could achieve historically.

I saw on the Wiki that subs have 0.5 to 1.5 anti-air. But I don't know if that's still accurate. In any case, it should be its own slot on the ship designer. Some subs had impressive anti-air armament.

I think the most AA a sub had was a couple of quad 20mm and maybe 2-4 37mm guns. While this is impressive for a sub, this was (for that time of the war), average to a-little-below-average AA for a destroyer without a main battery that could be used against aircraft.


These are the SS type in my post above. Thanks for sharing though - the Japanese sub nomenclature is reported differently in different places, and can sometimes be a bit tricky to follow. To make it even more confusing, they re-numbered a bunch of their earlier I-class subs during the war!


Ah, sorry, I left out the submarine oilers (as these were primarily used for refueling) - if we're including them, then you can add in 10 German Type XIV subs as well.


These are the Yu-1 and Yu-1001 classes above (although my numbers look like they're lower than 38 - I'll be looking into that and thanks for bringing it to my attention :) ). As per my comments on Japanese plans, these should be taken with a truckload of salt - Japanese build plans were often not realistic. For example, while they planned to build 6 Sen-Ho/I-351 submarine oilers, they only ordered 3.

And I'm sure there are many more.

My records are based on going through Conways All the World's Fighting Ships, 1922-1946 and Bagnasco's Submarines of World War II (and a bunch of other sources, but these are the 'broad sweep' books). While they may miss a few (for example, lower numbers of the Yu-1/Yu-1001 subs), it's very unlikely they missed 'many, many more'. If you want to check yourself, Navypedia is a good site with some pretty reliable numbers on warships (including transport subs) built.
 
I think the most AA a sub had was a couple of quad 20mm and maybe 2-4 37mm guns. While this is impressive for a sub, this was (for that time of the war), average to a-little-below-average AA for a destroyer without a main battery that could be used against aircraft.
Exactly, even the "AA trap" submarines had scarcely more AA firepower than a standard destroyer. In HoI4 for all intents and purposes Subs would have no AA.
 
Here's are more Transport submarines. In the game I imagine them functioning as very stealthy convoys that can resupply isolated small island garrisons which is what they did in real life. They wouldn't be able to resupply vehicles though.
There were the "magic carpet" imports to the besieged island of Malta, as well, but I think you'll find that all of these "submarine supply lines" weren't really providing a fully operational supply. They just didn't have the capacity. What I think they did achieve - and strategy games in general tend to be poor at representing this - was that they kept the "lines of communication" open. They may not have had a large physical/military effect in supplying significant quantities of ammunition or POL (petrol, oil and lubricants), but the morale effect of being able to supply something - thus proving that "home is thinking of you and can still reach out to you", can be quite profound. Maybe this would be represented by some sort of bonus for having some (any) naval units of your own side operating (even if dominated) in adjacent sea areas, or having operating air supply?
 
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There were the "magic carpet" imports to the besieged island of Malta, as well, but I think you'll find that all of these "submarine supply lines" weren't really providing a fully operational supply. They just didn't have the capacity. What I think they did achieve - and strategy games in general at representing this - was that they kept the "lines of communication" open. They may not have had a large physical/military effect in supplying significant quantities of ammunition or POL (petrol, oil and lubricants), but the morale effect of being able to supply something - thus proving that "home is thinking of you and can still reach out to you", can be quite profound. Maybe this would be represented by some sort of bonus for having some (any) naval units of your own side operating (even if dominated) in adjacent sea areas, or having operating air supply?
Given that these operations were basically standard operation procedure I don't think there would need to be specific game mechanics.
 
Given that these operations were basically standard operation procedure I don't think there would need to be specific game mechanics.
That's a valid thought, but the result of the "SOP" was to put assets at risk. Thinking about it, it also did provide some materiel advantage with small bulk items like medicines and electronics. Maybe all that's needed is some abstraction in the way of putting assets at risk for isolated units?
 
Does any negative modiffier for submarines when going out of fuel supply, i had zero stockpile as netherland in homeland after decolonizarion and while i hold my subs still make same sunk ratio per mounth. i check displayed variables and i dont find any modifier in any place.
I dont check in surface fleet. Does it have any negative modiffiers?