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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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I noticed that there was mention of special sub hulls for the Germans, will this also be true for the Japanese I400 or will they be part of the ship designer, i.e bombing craft/scout craft for non-german submarines?
300px-FA-330_Bachstelze2.jpg

This is the Focke-Wulf Fa 330 'rotary-wing kite'.
That is the 'spotter plane' employed by the German u-boats: One man, less than 70 kilos empty, less than 5 meters long.
And it had to be dragged by the u-boat since its own motor was not sufficient to lift it.
 
Plane catapults should:
-Decrease stealth (you know, being big fat box lobbed on top of the sub)
-Decrease maneuverability and speed (... big fat box, heavy airplane...)

I'm slightly confused, I can see that deploying the plane will help with detecting enemy, but it's not clear to me how will the plane itself not compromise submarine's position, both getting to air and landing???
The Fa 330 I menitoned above needed 5 minutes to put together, and 2 minutes to disassemble and pack away. Compare the extension of view range from 5 sm to 25 sm this means that even planes would only just catch the u-boat.
 
We´ve to talk about ressources .

Germany never ever had so much iron ore (and ships need lot of high quality steel):

In the year before the war, Germany received 22 million tons of iron ore from various sources. Although it was able to produce around 10m tons of its own iron ore each year, it was of low grade quality and needed to be mixed with high grade material from other countries such as Sweden, which annually supplied it with 9 million tons: 7 million from Kiruna and Gällivare in Lapland and 2 million from the central Swedish ore fields north-west of Stockholm.

https://en.wikipedia.org/wiki/Swedish_iron-ore_mining_during_World_War_II

In HOI game (at moment) iam able to sell my steel to other nations if i play as german.
 
Good DD
 
Is there a chance that submarines could be split into 2 specialised trees?

Costal and Deep Water Submarines?

Something similar to how the Superheavy Battle Ship tree branches off from the Battleship tree.
That is a really good idea.
 
The Fa 330 I menitoned above needed 5 minutes to put together, and 2 minutes to disassemble and pack away. Compare the extension of view range from 5 sm to 25 sm this means that even planes would only just catch the u-boat.
First of all, I would like to thank you, despite more then two decades of interest in military history (especially ww2) I have not run into this vehicle yet, it's very interesting.

That said, I don't think that this is what the hydroplane module is supposed to represent. And of course the combat record is rather unimpressive.
 
More important is how the scorts works, they should be assignated to the routes and no a "zonal potrol of convoys". Darkest Hour convoy raiding would be no very deep, sure its no the best, but DD as patrol work as patrol, DD as scorts works as scorts.
Actually, escort groups were typically assigned to areas, and then to particular convoy passing through that area. This makes lot of sense given the restricted range of more common u-boat classes, and of course limited amount of escorts available.
But of course one wonders how will it work with multiple convoys, multiple sub groups, multiple escorts - if they will all pile up in single combat in the area, or if there will be multiple combats there...
 
Which is?
One sinking attributed to the plane spotting the target (somewhere near Madagascar).
You can theoretize that it may possibly have helped the sub to escape in some cases, but this would only be the case in areas with very limited presence of allied aircraft. Using it in channel would be completely nuts, considering subs are visible some depth bellow surface and depth charges can be used to attack.
 
The torpedo reveal chance looks like it could be an interesting thing for people who'd want to model things like the difference between steam torpedoes and electric ones.
 
Looking at the losses it seems they do well against obsolete destroyers but I doubt they will be that strong against modern destroyers with good detection and ASW Equipment, but it takes time to get those which give the submarines a head start.

Seems historical. . . U-boats dominated the Atlantic the first three years of the war. Even sinking merchant shipping in sight of the US coast and into the St. Lawrence River.
 
Finally, my U-boats will actually DO something.
 
This is the Focke-Wulf Fa 330 'rotary-wing kite'.
That is the 'spotter plane' employed by the German u-boats: One man, less than 70 kilos empty, less than 5 meters long.
And it had to be dragged by the u-boat since its own motor was not sufficient to lift it.
Mate, I don't understand your point?

I'm wondering whether the aircraft catapult planes or modules mentioned in the dev diary are German submarine specific.
Because there are several aircraft carrying submarines prior to or during world war two, like the I-15 class with the E14Y 'Glens'.