The unreasonable effectiveness of submarines

[bitmode]

I sank an assload of destroyers and convoys, but the bigger ship eluded me.

For some reason, subs have a much higher targeting priority against convoys than capitals (https://hoi4.paradoxwikis.com/Naval_battle#Target_selection):

• capitals: 30
• [...]
• submarine vs convoy: 600

despite an individual convoy being worth much less and having comparatively lots of HP per IC.

 

[DicRoNero]

For some reason, subs have a much higher targeting priority against convoys than capitals

I would suggest the reason was to make current mechanics "work", i.e. make subs hunt convoys rather than overpower surface ships in the way the OP does.

The submarine warfare is full of ad-hoc half-baked solutions anyway. My favourite one is probably a bunch of WW1 rifles taking a whole armada of convoys to get transported.

 

[Orbs]

The way to get these results reliably is to do everything to reduce your sub visibility and your torpedo reveal chances. For this particular game, I gave Donitz "Silent Hunter" and then the next two sub promotions, I maxed out the right branch of the trade interdiction, I used the sub naval design company, I researched electric torpedoes, and obviously I used 1940 subs with snorkels. Just stack all the torpedo reveal modifiers, visibility modifiers, and then attack modifiers (the more attack you have, the quicker you dispose of fleets to move on to the next one, as sometimes you can get stuck in a bottle for a couple of months).

Thank you!

As Italy you don't really get a commander who can get the Sea Wolf option at start (at least not that I saw), so I had to farm for it and it definitely took a while. That gave me the opportunity to see how effective this is both with and without that trait (and subsequent traits).

At the beginning of war with the Allies in 1939 (and thus war with France and UK - No US yet) I was able to get 1940 subs along with sub tech Snorkel, Electric Torpedo and Magnetic Detonator. I only had commander skill Concealment Expert. I also did the Trade Interdiction doctrine about 3-4 down the right side (at war start).

The subs were still very effective at killing screens and convoys, with the occasional capital ship (heavy on the occasional). While I didn't get results like the above screenshot with this set-up in 1939, it definitely made life easier, especially if my strike force joined the fight. Controlling the Med was a lot less terrifying.

After getting Sea Wolf, Silent Hunter and Loading Drill Master skills for my commander, along with Snorkel 2 and Homing Torpedo, my subs were unstoppable. The only issue I had is that once again capital ships were still getting away more than I wanted, but I was definitely getting more and more of them during each battle, and if they did stand and fight (like the IJN did here), then it was sink city.

 

[Gort11]

This strategy works best in deep oceans, by the way. You'll take many more losses if you try it in shallow waters like the English Channel.

My favourite spot is Cap Verde - tons of traffic goes through there and it's deep ocean, a long way away from any enemy naval bombers who'll whittle you down.

 

[Harin]

Thank you!

View attachment 651564

As Italy you don't really get a commander who can get the Sea Wolf option at start (at least not that I saw), so I had to farm for it and it definitely took a while. That gave me the opportunity to see how effective this is both with and without that trait (and subsequent traits).

At the beginning of war with the Allies in 1939 (and thus war with France and UK - No US yet) I was able to get 1940 subs along with sub tech Snorkel, Electric Torpedo and Magnetic Detonator. I only had commander skill Concealment Expert. I also did the Trade Interdiction doctrine about 3-4 down the right side (at war start).

The subs were still very effective at killing screens and convoys, with the occasional capital ship (heavy on the occasional). While I didn't get results like the above screenshot with this set-up in 1939, it definitely made life easier, especially if my strike force joined the fight. Controlling the Med was a lot less terrifying.

After getting Sea Wolf, Silent Hunter and Loading Drill Master skills for my commander, along with Snorkel 2 and Homing Torpedo, my subs were unstoppable. The only issue I had is that once again capital ships were still getting away more than I wanted, but I was definitely getting more and more of them during each battle, and if they did stand and fight (like the IJN did here), then it was sink city.

Thanks for sharing your results. I do have one question, since you said capital ships were getting away. Were you using Always Engage for your subs, so the subs do not retreat? I read above how that is important, since the capital ship fleet may not see the subs as a threat and will stay in the fight and it is the subs that may be retreating.

 

[Sbrubbles]

Interesting stuff. I was always using mass naval bombers to whittle down AI fleets (which the AI also doesn't really know how to deal with), but I guess subs are even stronger.

Given the power of naval bombers, I wonder if an efective way to deal with enemy subs is by parking something like 5 carriers in a sea zone (with reasonable escort and no mission) and letting the planes out to do their thing at no risk. A human player could theoretically notice their subs dying and use a few patrol missions to find the fleet then engage with subs, but I wonder how long that would take or how effective that would be.

 

[Orbs]

Thanks for sharing your results. I do have one question, since you said capital ships were getting away. Were you using Always Engage for your subs, so the subs do not retreat? I read above how that is important, since the capital ship fleet may not see the subs as a threat and will stay in the fight and it is the subs that may be retreating.

Yup I should have included 2 more important pieces of Information.

1. My 1940 subs were set to Always Engage, and were doing very well, but capital ships were mostly getting away (I would catch some on the odd-occasion, and also some more if my subs were able to catch that fleet again immediately after the battle ended). One other important factor I noticed in many of the battles was that the 1940 subs were indeed damaging the capital ships, but not damaging them enough to sink them before the engagement ended.
2. The other important information that I should have included, and regret not doing so (so thank you for giving me the opportunity), is that when the war started, half of my sub fleet was 1936 subs, and I didn't want to just let them rust. So I set them to engage at high risk (instead of always engage) and I got to be honest, they did pretty darn good too. I was very careful to not have any mixed 1936/1940 wolfpacks. They were either all '36, or all '40.

To clarify, when my 1940 subs engaged, I didn't really lose any (maybe 3-4 total while I wiped out the combined British/French fleets) and they definitely killed things (especially screens and convoys as previously noted). I lost more 1936 subs by far, and they didn't kill as efficiently obviously, but I would totally use them again. In fact I would definitely invest in building the 1936 subs again until the 1940 variant became available. The thirty-sixes were disruptive, sank more than they cost (or were worth) to me, and were absolutely an integral part of winning superiority in the Med. In fact it's 1944 now in my game and I still have thirty-sixes sinking Japanese and American convoys

Not sure if this matters (probably does), but I also tried to have my wolfpacks in groups of 20 at all times (for both the 1936 wolfpacks and the 1940 wolfpacks). Maybe that's why the 1936's did ok? Or maybe that's why I was having trouble really killing the capitals? I'm not sure, maybe someone knows.

EDIT:
One more opinion to share. This sub strategy is so strong that I stopped building surface ships. In my view, there's really no point in having a surface navy if you go this route. These subs are just so much more efficient at killing everything, they rarely take damage, are more fuel efficient, have longer range and require less resources AND less IC to build. You can simply demolish any major fleet, wreck everyone's convoys to the point that everyone actually runs out of convoys, and can establish naval superiority virtually across the globe.

The only thing I don't know at this point is how to kill other subs with this approach, other than just using naval bombers?

 

[Sbrubbles]

Yeah, other than just using naval bombers, I have no idea.

After looking at the wiki and a few other threads, it seems to me that the problem is that the bulk of the probabily of finding a sub in-battle comes from them firing a torpedo (which happens every 4 hours), which is independent of the other side's sub detection and can be brought very low through techs and admirals.

There is a probability of finding a sub in-battle that is a factor of sub detection, but not only is this probability pathetically low in the best of circumstances, but it seems to rely on average sub detection of the engaging fleet, so if your spotters engaged and your main fleet comes along, this probability suddenly plummets.

Am I right in this or am I missing something?

 

[DicRoNero]

So, has anyone so far been able to mod this blasphemy out?

(without breaking anything else, that means)

 

[goodcigar]

One very big problem I have with naval gameplay is bad feedback from game. It very hard to understand what happen in a naval battle because the game does not show you an hour by hour - play by play breakdown of the battle. It only show you the end result. So you have to guess what happen.

HOI4 not have good quality feedback since day one 2016 imo.

 

[DicRoNero]

One very big problem I have with naval gameplay is bad feedback from game. It very hard to understand what happen in a naval battle because the game does not show you an hour by hour - play by play breakdown of the battle. It only show you the end result. So you have to guess what happen.

HOI4 not have good quality feedback since day one 2016 imo.

The worst thing is that the UI doesn't even bother to show you there's a winning/losing battle in progress - just 'a battle'. So if you start off a convoy hunt and an enemy surface fleet pops up in the same battle while you're preoccupied with other matters you are likely to remain unaware of it until either party is already at the bottom of the ocean feeding crabs and mollusca.

This favouritism for land warfare is just disgusting. In land war, the game notifies you even if your most poorest CAV division ends up in trouble.

 

[Caeric]

Frankly, what all this tells me is that the game badly needs a cheap escort hull that isn't just a stripped down early DD. Destroyer Escorts, frigates, corvettes etc. had a fraction of the tonnage, could be constructed a breakneck speed and some form of similar craft was pretty much in service with almost all the major navies.

Just give them better detection values than interwar ships and the bare minimum slots but a few hundred less IC cost I guess.

 

[balmung60]

As long as they dont get nerfed to uselessness like they were before.

Hot take, but I'd rather have useless subs than have subs make everything else useless.

 

[DGuller]

I don't even bother with earlier subs in battles. Maybe I use them as mine-layers, but honestly I don't bother anymore, I can dispose of fleets just fine without mines. I use them for training but then delete them once I'm up and running with 1940 subs.

I recently realized that by eschewing pre-1940 submarines and not using them as mine layers, I was missing out on some devastating synergies. If you mine the waters, the subs will pulverize the destroyers much more quickly, since I assume destroyers will be very slow and unable to dodge torpedoes. Once the destroyers go, the navy goes. This isn't really surprising, but it just didn't register with me how much more effective an already overly effective strategy can be if you add minelaying to the mix.

Normally this would be overkill, but in certain situations where you want to alpha strike quickly, this could be crucial. In particular, I use subs and minelaying to quickly DOW and annex Japan as USSR, before the war with Germany starts. You only have a narrow window to do that, so you want to delete the Japanese navies ASAP and seal off the island before divisions from China rush back to defend. By taking out Japan, you keep the US from joining the Allies, which leaves you with the option of annexing UK sometime in 1942-1943 if you feel like it.

 

[guachi]

Just give them better detection values than interwar ships and the bare minimum slots but a few hundred less IC cost I guess.

To keep the screen from being cluttered with hundreds of small ships the destroyer escorts and frigates could be rolled into the abstracted convoys.

Though maybe a dedicated ship would be better. It would still require the AI to research and build them.

 

[Caeric]

To keep the screen from being cluttered with hundreds of small ships the destroyer escorts and frigates could be rolled into the abstracted convoys.

Though maybe a dedicated ship would be better. It would still require the AI to research and build them.

I doubt that would be a problem unless the AI does spam them. As lighter even than very small destroyers, their lack of hp and armor coupled with not having very good evasion from being a bit slow would make them effectively just cannon fodder in a surface engagement even against DDs and quite vulnerable to attrition from aircraft on naval strike missions.

Even with a lower price than even the most barebones DD it's not quite the level that you could realistically flood the ocean. They should only realistically be a solution to achieving more coverage for the oceans for cheap without completely screwing you out of all other naval production instead.

 

[AFilthyCasual]

I don't see why it can't be like it was in older games: you built escorts, and they were auto-assigned to convoys.

There should be DE and CVE hull-types to build, but rather than going into your navy, they're considered part of the convoy, along with the actual transports.

The fact Panzerschiffe and Coastal Defence Ships get dedicated hull types but Destroyer Escorts and Escort Carriers don't is Eurocentric - specifically Continent-centric - silliness. I'm Canadian, I should know, 95% of our navy was convoy escorts.

 

[Louella]

I've thought about a corvette/frigate/sloop/destroyer escort hull, that would be cheaper and slower than the smallest true destroyer hull, but with 2 slots for sonars/hydrophones. I thought that would give it enough detection to be useful.

the hard part is figuring out how to get the AI to build them without getting silly.

 

[GrandVezir]

the hard part is figuring out how to get the AI to build them without getting silly.

That's the crux of nearly every problem in game.

And lest we all forget, the reverse is also true: it's hilariously easy to defeat AI submarines.

Want to take out AI submarines? Build a bunch of these:

Spoiler

That's all 1940 tech, so upgrade it to '44 if you feel like rushing. Put a suitable admiral in charge:

Spoiler

Not perfect, but he'll do. This fellow deleted the IJN submarine forces in 1936-1937 and the combined Allied submarine forces by 1942 -- except he was only using 1932-1936 tech, so it could have been quicker. He's currently rolling with eight task forces that look like:

Spoiler

The cruisers are basically just there for their spotting planes. Pick all the best escort doctrines (left branch on Base Strike or center on Fleet in Being for the UK) and watch the AI submarines go away.

 

[AFilthyCasual]

I've thought about a corvette/frigate/sloop/destroyer escort hull, that would be cheaper and slower than the smallest true destroyer hull, but with 2 slots for sonars/hydrophones. I thought that would give it enough detection to be useful.

the hard part is figuring out how to get the AI to build them without getting silly.

Making it a separate hull type rather than a modification of destroyers might actually make it easier.

The AI doesn't do well with micromanaging templates, modifications and such, just look at their division templates. It needs simple categories; this is why the Expert AI mod railroads the AI into building 6 pre-made division templates - an anti-partisan unit (just one CAV battalion since LaR), a garrison brigade, an infantry division, an armoured division, a motorized division, and either a Marine or Mountain division, all of a usable combat width (10/20/40). That's it. Anything more complex or fluid than that fucks it right up.