Watch me get all extra pedantic about it… :-D
I don’t think the distinction between tactics and strategy is very useful in A&A sometimes, as it seems to result in confusion for people. Both modern words come from ancient Greek terms, common use terms, the first via Latin, the latter directly.
Taxis-Taktikos in ancient Greek means “arrangement”, taktike is the abstract feminine noun for “arrangement”, taktike tekne (from which Latin “tactica” derives) is someone’s “arrangement skill” or the “art of arrangement.”
Strategy comes from the ancient Greek word for “General.” Strategy is something that a general does, with his forces en mass, whether its skillful or artful, depends on the general I guess haha
A Strategos like Xenephon, might use his taktike tekne, to throw up blocking maneuvers to cover a retreat, in order get his army safely back to the sea. The distinction in the modern sense, comes down to whether the tactic serves some broader purpose or goal for the militarist. The french tried to introduce a greater degree of nuance into the terms, but in A&A basically everything you do is a conflation of these terms. Usually in the strict sense, its just a matter of scale. Or put another way, how high you want to aim.
For our purposes tactics are things you do to react or exploit opportunities in the moment, or the heat of battle, in a given round. Strategy is something you do over time, building across multiple rounds.
A single destroyer blocking a single US fleet movement in a given round, is a tactic. But buying a bunch of destroyers every round and constantly leaving them to block US fleet movements for the duration, is strategic. In this case, the strategy is to disrupt the enemy’s naval combat movement ability, to win control of the ocean as a way to win the war. Is that what you mean madscientist?
I think in the long run, if you pursue this kind of constant blocking strategy, you will end up being defeated. This is because destroyers are relatively easy to kill with aircraft, that have more movement points than ships. That doesn’t mean its a bad idea to buy destroyers, but it might not be the best idea to constantly put them at risk just to disrupt USN movement. Sometimes a block might be really critical, in which case the cost of a dead destroyer becomes totally worth it. In a discrete instance like that, a destroyer block would usually be described as tactical, in the way Herr KaLeun tried to point out, and it might be a great idea. Or it might not, depending on the circumstances.
But if you’re buying DDs every round, in order to sacrifice them as blockers, in the strategic sense, then you’re probably going to lose out in the TUV trade in the long run, esp. if your opponent is trading subs (paired with air) to kill your Destroyers. Since his fodder will be cheaper to replace than your blocker. There’s also a good chance his fodder sub will survive against a single destroyer. Also as Herr pointed out, to truly block USN movement, you need to block it in both the combat and non com phase, which means leaving surface ships to occupy all the sea zones along the non combat paths too, and that the gets expensive. I’ve seen this sort of move described as destroyer “fanning” or “picketing.” This tactic could work sometimes when the opportunity to restrict the USN is very critical, like in blocking an amphibious assault
In the broader strategic sense though, its better to conserve your Destroyers and set up for counter attacks. Rather than disrupting the USNs ability to move, you save those units for major counter attacks (deterring the USNs movement in the first place, for fear of total annihilation, rather than blocking it), and then only use naval units to block when it really matters.