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HOI4 Dev Diary - Mines and Minesweeping

Welcome to another glorious Wednesday! Today we are going to be talking about mines and mine sweeping. Historically hundreds of thousands of mines were laid during WW2 and with Man the Guns you too will be able to do so in Hearts of Iron.

From a gameplay perspective mines do a lot of interesting things. They add more interaction with the naval layer of the game, create a weapon both for smaller naval nations to fight bigger ones, and for big ones to try and limit where the enemy can get to them.

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As you may remember from my presentation at PDXCON, I talked about adding a ship designer to Man the Guns. It is not quite ready to show off, but it’s important to know that sweeping and laying mines are something you will be upgrading or redesigning your ships to be doing. Minelayers and Minesweepers are not actually new ship classes. In my screenies I have destroyers that can both lay and sweep mines for simplicity, but as @Archangel85 pointed out earlier “I am probably going to have a ton of different destroyer designs”... anyways, details on the designer is for a future diary when it is done, but hopefully it helps explain some stuff in the proper context.

Mines are unlocked from techs and require ship designs fitted to deploy them. Destroyers and light cruisers can do this, as well as submarines with the correct tech (excellent if you as Germany want to make things even more dangerous for the British at a lower risk to yourself). Mines can also be dropped from the air with later game techs. Both of these unlock new missions for navies and airwings.
mine_techs.jpg


Mines can be made better and better through research. You start off with Contact Mines to unlock them. Then their destructive power is improved with Magnetic and Acoustic mine techs and finally with Pressure mines. At the bottom (heh) you also see two techs for submarine mine laying. The first is just the basic ability, while the second improves efficiency a lot by allowing mines to be deployed through torpedo tubes, thus no longer requiring you to design specialized minelaying submarines.

To get rid of mines you need minesweeper capable ships. This unlocks the naval mission to sweep mines and will slowly work at clearing areas. Minesweepers are also nice to include in your fleets as they will then be assumed to travel ahead of the fleet and reduce the impact of mines on them. I suspect a good design combo will be anti-air and sweeper on screen ships to be your passive defense when in enemy waters.
mine_report_map.jpg


There is also a passive “degaussing” technology that can be researched after Magnetic Mines. This was employed during WW2 to reduce the magnetic signature of ships and thus make them less likely to set off mines.

It is also possible to sweep mines from the air, but this is a late game, expensive technology and unlocks a new air mission for bombers. This was something that was done sparingly and in shallow waters, but for example was successfully done to evacuate the Dutch royal family to Britain.

What do mines exactly do then? Well they blow stuff up! Their explosive results are shown on map as accident reports, and there is a new tab too under the Naval Losses statistics interface if you want to dig into details. As ships operate or move through a zone they will risk running into mines. This can lead both to minor damage as well as outright sinkings. The best ways to avoid this is to make sure the area is swept free of mines, but as mentioned above, having your ships travel with sweeping capable ships makes it safer for all.

mines report.jpg

This is not all through, mines have several passive effects.

Naval superiority - Having mines in an area helps amplify the effects of your navy (after all they can concentrate more effectively knowing where the mine fields are). This can be seen in our new naval area screen, which is the naval equivalent of the state view:
travel.jpg


Other than that and blowing ships up mines will slow down enemy ships (since they need to be more careful) and increases the invasion penalty to coastal area. So mines are both good offensively and defensively.

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Mines can only be laid while at war and will start to disappear over time once a nation is completely at peace. You always know how much mines there are in an area, so you know how to deal with them and take them into account. That means that with the new naval access controls you can tell your ships and convoys to avoid heavily mined areas, but of course this may make it a lot more predictable for your enemies where to hunt. Having an advantage in the encryption-decryption war will also add a certain amount of passive defense against mine effects as you may have some information about their positioning.

See you all next week for more Man the Guns info!

Rejected Titles (for extra good reason this time...):
- This War of Mine
- Vengeance is Mine sayeth the Lord Admiral
- Do you mine’d
- This feature was made in cooperation with the seagulls from Finding Nemo
- Mine = blown
- The Ship Designer isn’t unfinished, it’s just a bit shy
- Minesweeper 2000 Online HD Edition
- Mine over Matter
- Mine the guns
 
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Other than that and blowing ships up mines will slow down enemy ships (since they need to be more careful) and increases the invasion penalty to coastal area. So mines are both good offensively and defensively.
Will mines potentially do damage to divisions performing naval invasion, as in damaging transport ships?
 
What happens between wars, in the case when Axis is destroyed and the SU declares against the Allies. Usually this happens pretty quick, and mines were an issue for countries for many years after the war. Having them just disappear seems wrong.
This can be seen as an abstraction of all mine fields on both sides made public and known to shipping, allowing mined areas to be avoided and for save routes to be created for merchants and warships alike. Post war minesweeping just seems like useless micro, and minefields degrade naturally anyway.
 
Will there be any changes to the way actual naval combat works in regular naval battles?
yea, but its a lot of work, so its going to be fully explained quite late in the development of MTG

Is mine laying tied to swallow water, or can you place mines in all naval terrains?

we'll go over that when I talk about naval terrains. but yeah you can place them wherever. some places may be more strategic though

Why did you decide, that mines should completely disapper once a nation is on peace?

It just seems a little bit strange, could you please explain it to us? :)
A few things - I know that the cleanup was a big deal in reality, but doing it like this avoids tedium of cleaning up in peace time. It fixes a bunch of exploits and stops numbers from going truly wierd for a 3rd world war. especially with sides swapping allegiences and suddenly not being aware of where mines are etc (as noted above. stuff tends to be made public). I didnt feel it would add very much. I mean technically we could have a fast decay instead, but I wasnt convinced it would really come into play and be worth the effort.
 
Can you lay mines in peace time and if so will they affect neutral countries and will there be restrictions on when/where you can do it?
no, war time only. I think there are still some pretty heavy laws against that
 
In WWII, how many warships were sunk by mines?
It was extremely important in the Baltic Sea.
The Soviet Baltic sea fleet which was not insubstantial (contrary to popular belief) especially as Kriegsmarine wasn't glorious either was basically crippled by mining not only in losses but also having to camp in ports and such.

As for total numbers this looks nice
https://www.naval-history.net/WW2CampaignsMineWarfare2.htm
Pg2cfU2.png

if their numbers are accurate (there are some sources mentioned on site), only allied ships though. In 1940 its even second place after subs.
 
IMPORTANT:

Mines dont know friend or foe.....

Example:

- The war is over but the mines will stay in effect (cause theyre not removing alone)
- Germany at war with UK (and both nations laying mines northsea). Result: All ships including those of nations NOT at war could be sink if theyre in that area (including freighter)
- The nation that decide to lay mines must face huge penalties even to neutral nations (if iam neutral why i should send my ressources to a nation at war if i risk to loose my ships by sea mines? I wouldnt, of course that could inflict massively raising prices)
- If Mexico at war with Cuba and Cuba decided to lay down mines all over caribic be sure USA would immediatly declare war if a number of USA ships sunken by Kuba sea mines (as told mines dont know friend or foe)

Please share your thoughts and reply....but good idea , that will need a lot more work than just to add mines and of course its neccessary (oh iam a magnetic sea mine and this ship is my friend i wont explode.....that is NOT allowed)
 
IMPORTANT:

Mines dont know friend or foe.....

Example:

- The war is over but the mines will stay in effect (cause theyre not removing alone)
- Germany at war with UK (and both nations laying mines northsea). Result: All ships including those of nations NOT at war could be sink if theyre in that area (including freighter)
- The nation that decide to lay mines must face huge penalties even to neutral nations (if iam neutral why i should send my ressources to a nation at war if i risk to loose my ships by sea mines? I wouldnt, of course that could inflict massively raising prices)
- If Mexico at war with Cuba and Cuba decided to lay down mines all over caribic be sure USA would immediatly declare war if a number of USA ships sunken by Kuba sea mines (as told mines dont know friend or foe)

Please share your thoughts and reply....but good idea , that will need a lot more work than just to add mines and of course its neccessary (oh iam a magnetic sea mine and this ship is my friend i wont explode.....that is NOT allowed)

Normally nations will warn, or tell allies and people transfering shipping so as to not explode. while I am sure there were mistakes we felt the simplest and easiest way was to make sure you couldnt hit friendly or neutral mines and were abstracted to steer clear.


neutral nation mining along your coast in another war kinda would be cool as a reason to justify war tho I agree
 
not sure on count, here is a wiki link: https://en.wikipedia.org/wiki/Category:Ships_sunk_by_mines


- sweeping works just like laying mines, so you slowly reduce them. not all at once
- atm "size on map" isnt a factor, but there are other things that play in here. see a future diary when we go over "naval terrain"
I already saw that Wiki list before I posed the question in here. The Wiki list includes ships going back to the US Civil War.
 
I also like @happy60922 's idea for this to be done by event as well!

Thanks - I can think of some good 'special projects' that could be done via command and reflect operations in areas of special mine laying interest that would be fun to mod in - if we get the command that is. On that ilk, @podcat, are there any plans to add back the nuke command for us modders, so we can fire nukes through events etc too?
 
I saw that Wiki link before I posed the question in here. That Wiki list includes ships going back to the US Civil War.
yeah I was lazy ;) there was some other decent numbers quoted in the thread too.

A smart player is honestly not going to field their whole fleet in heavily mined areas if they can help it I think, so even if they do not directly sink a ship as often as they could in the game, they will have an impact on where and how stuff operates
 
future dlc in my dreams....

I was actually thinking more of the tense moment where a math person found out that Germany was going to sink a ship, via U-sub, that this person had familial relatives onboard and wanted to warn them off.

But sure it can also ties into espionage.