Slitherine

Lets discuss convoy aspect of naval warfare. I think destroyers become deadly vs subs way to early.

Historically uboats became 'ineffective' after Black May in 1943. In game it is rather suicidal to go for escorted convoys as soon as late 1941, with hits from British DDs like 1:5.
Probably ASW scaling should be made less steep? Or subs should get more experience for their early convoy hits, as soon enough there will be little or no targets of opportunity. Maybe I am the only one experiencing this (both Axis and Allied games)?

If you are gonna make them weaker then the Brits should start with more of them so that unescorted convoys are a rarity (6 in the atlantic instead of 3). I find the subs way too powerful. Another thing is that subs should only be able to attack a DD once (like a ship in port) unless a surface ship starts the combat. Herds of subs can sink DDs too easily.

Actually, it's surprisingly easy to destroy DDs early on (usually before the start of Barbarossa), because a single DD rarely survives an attack by 3-4 subs. It's only the first and the second attacks which are rather harmful to subs. When a DD loses efficiency and some steps, it becomes harmless.

If you are gonna make them weaker then the Brits should start with more of them so that unescorted convoys are a rarity

I disagree. That would unhistorical and bad for balance, too. IRL one of the biggest challenges for U-boats was finding the convoys. Remember that the ocean is ridiculously big, so that wasn't easy. On the other hand, most convoys were unescorted, because the UK didn't have enough escorts to cover every convoy. I think that these things are quite well represented in-game ATM.