The nearest odds OOB “Destroyer on offense” configuration is actually:
Group 1 DD A1 D2 C6 Attack Depth Charge 1,
61% DD win compared to 60% OOB
The nearest odds OOB “Destroyer on defense” configuration is actually:
Group 1 DD A1 D2 C6 Attack Depth Charge 1,
73% Sub win compared to 88% OOB
This seems interesting but it is only relative to Subs vs DDs
Even with same cost and similar combat values,
Subs A2fs D1fs M2 C6 are now more powerful than OOB Subs due to always first strike and not blocked by Destroyer.
So this new Sub is a bit more powerful than Cruiser, Carrier and Battleship. But it is not the main issue.
Above of all, because it is same cost than Destroyer, Submarine compete with Destroyer as fodder unit.
I can easily imagine that on defense, Submarine would be taken as casualties mostly coming from attacking’s Sub successful hit.
Simply because both attacking and defending get their roll, while Destroyers still have to roll.
Naturally, it is better to maximize number of rolls per combat round.
So, it can be circumvent whether by a lower cost for Destroyer (5 IPCs),
or a special player enforced rule: “Submarine must be taken as last casualty amongst warship.”
Or both.
Using 5 IPCs A1 D2 M2 Destroyers directly decrease other warships combat power, especially on defense (OOB D2 cost 8, now it would cost 5).
Hence, it is a call for a DD5, SS6, TP7, CA9, CV12, BB15 cost structure.
Otherwise, (if Triple A cannot manage to “forbid Sub to hit Sub”, as Barney told us) it requires that we agree to try it with the special rule:
Submarine must be taken as last casualty amongst warship.
That way, it may be balance to work on DD A1 D2 M2 C6 ADC1 (which is consistent with the basic 2 IPCs give 1 combat point or 2:1 IPC/pt ratio for Naval unit).
However, I strongly believe that Cruiser M3 C12 and Battleship 2 hits C20 needs stronger boost to be balanced with Destroyer A1 D2 C6.
Here, I’m thinking about AA capacity (which can be done in Triple, Barney proved us.)
And even something more or different for Battleship (1 Inf carrying capacity? an increase Convoy Raid of 2 Dices as Subs? other?).
On the other side, Destroyer should no more be able to Convoy Raid, because, on same IPCs basis, it means 3 Dice compared to 1D6 for Battleship.
An issue remains about planes on attack.
They appear also weaker attack per cost ratio compared to Destroyer.
DD at 5 IPCs is extreme but 6 IPCs DD can still be an acceptable issue since many people complain about Fg being too cheap or OP.
Here, my single adjustment to 6 IPCs DDs should be on Tactical Bomber A3-4 D3 M4-6, TBR A1 D6 damage and A1 Depth Charge, cost to be put at 10 IPCs.
This would slightly increase the attack ratio of TcB compared to Destroyer.
But, contrary to OOB, now Destroyer are much more cost effective against planes.
Finally, keeping Subs and DDs at 8 IPCs is also problematic.
It takes 25% more IPCs to feed SZ in basic Naval units.
This will not help increase Naval interactions.
It can be suggested : DD C7 Subs C8 IPCs or DD C6 Subs C7, but need a few more AACalc comparison to find which is better.