Throughout World War II destroyers were used to provide point blank support to amphibious landings. Examples are the D-Day invasion, the Guadalcanal campaign, as well as the Tarawa and Iwo Jima landings. As a result they should be given small attack values towards infantry, armored and infrastructure to reflect this role.

A small attack value would not negate the effectiveness of cruisers and battleships. Just as in World War II, when destroyers were used to provide point blank support, cruisers and battleships were also used since they were more effective. In no way did the use of destroyers negate the usefulness of cruisers and battleships in the actual conflict and providing them with a small attack value in the game would also in no way negate the usefulness of having cruisers and battleships on hand.

Regardless, it doesn't reflect the historical role the destroyer played in the actual conflict. They were often used for shore bombardment.

Ok, let's run the numbers. Suppose we give destroyers the same land/infrastructure attack value as an AA gun (2). This is not a stretch since most destroyers guns were 5" and the most well known AA gun was the German 88mm.

Here is what would happen if you tried to spam destroyers. To have the firepower equivalent to a BB you would need 22 destroyers. As you can see below for the cost of 22 destroyers you could have a BB at roughly a sixth of the cost of trying to spam destroyers. Coupled with this the need for suitable production facilities to spam that many destroyers it becomes nearly impossible from a logistics perspective to do so. When one also considers the attack range difference there is really no reason to spam destroyers as it is is a waste of resources in comparison. Not only would it take vastly more time to produce 22 destroyers, there is no economic or military reason to warrant it.

........Goods Manpower...Metal....Oil....Rare_Materials...Money...Land/Infrastructure_Attack_Value...Attack-Range
DD - 1000......250.......1750....300............0............3000....................(.2)...........................20km
BB - 4000......600........4000...1250...........0............8000...................(4.4)...........................50km
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22DD - 22000..5500......38500..6600...........0............66000..................(4.4)...........................20km