Are subs utterly useless?

[Surt]

First, stockpiles don't need to be zero. Convoys should not take more ships to run to longer distances, but more time to arrive. And the AI would not be given any instruction: stockpiles would have a different threshold, period.

I don't understand what your mean here, more time to arrive must use more convoys?
So if you have one more day of travel because of longer route you will need 2 days (1 day to and one back) worth of convoys more to service this route?
So if it takes a whole transport worth of ships to contain 1 days worth of resource production you would effectively need 2 transports more for every day long route. Needing around 20 persons total.
The round trip for transports at this time is significant longer than modern time. A modern container ship take 2 week for a round trip New York to Manchester, 1 day in port and 6 days transit. During the war time the ships sailed much slower due to convoys so it too around 2 week transit and the loading/unloading took a week (if only doing one of them) and many times more men as they didn't use containers, for a total of 6 weeks roundtrip. Needing 100's of people.

 

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I did some addition recently on my total kills vs my total losses. A lot of convoy ships of course were in the mix. As Japan using a fleet of over 50 subs. I've lost a lot of them now actually, but I sank as much tech into subs as I could they aren't expensive at all manpower .4 and can't remember IC costs but my IC is enough to handle building tons of whatever at the moment I'm almost at a 800 tech due to upgrades and taking Russia and National china. I'm in 1942 now my kills are 422 vs losses of 124 thats almost a 4 to 1 ratio. Now this isn't all transports I just included them in there as well to make myself feel more invincible lol. But a lot of them are transports. But I've pretty much single handedly taken out the UK's navy and US pacific navy. The AI on hard is pissing me off though now because it will build hundreds of screens and subs and deploy them now they are causing serious losses to my air power and damaging my cap ships highly irritating. They don't have any real capital ships left is probably why the Ai is doing that. My answer was to amass my BBS into groups of a dozen or so with over a dozen screens and that is helping but they are causing attrition to my BBS still. But they are racking up the kills at least. But sending airpower is pointless they get chopped to swiss cheese in an hour against all of that AA firepower. Thats how I killed all of those Cap ships in the first place I guess thats an adaptation of the AI maybe?