Absolutely correct, in RL destroyers could locate submarines.
And in contrast, submarines could attack unrecognized without being tied up in close combat; here in the game, however, an attack will set them in melee.
..and after an attack subs could (try) to disappear in every direction they wanted and also in different depths; here in the game, however, there are only the given and known sea routes and no different depths.
But, since CoW is not a simulation all units are more or less adapted for better playability as a browser-(board)game.
Imagine, submarines could strike suddenly and from deep as in the RL and disappear unrecognized -- would be an extremely unsatisfactory game (and a lot of lamentations of many inexperienced players would be foreseeable) ..
..therefore subs are adapted and have only "melee torpedoes" and have to surface to any attack and are visible at surface for the full combat time ..
..and to compensate this enormous but necessary disadvantage of the submarines also their hunters was adapted.
So you have to look at destroyers, submarines and naval bombers in context. >> The naval bomber is the only one who can locate submarines, but if he attacks, he suffers AA damage from the sub/s (because fights with airplanes are mathematically always close-combats); The destroyer can not locate the submarine, but he can fight a located one from distance without suffering own damage. >> The naval bomber locates and the destroyer fights -- stone, scissors, paper >> strategy at its finest -- was it once before ..
..but in the past, this fine stone-scissors-paper-strategy has been softened more and more in favor of a hammer-on-anvil-action-tactic by extremely lowering the AA of subs what makes them an easy prey for naval bombers -- even without destroyers help ..
..so please don't ask for or bring in more disadvantages to the submarines, because subs are already still now nothing more than lame patrol boats.
But, on the other hand, if you really whish that destroyers must to be able to locate submarines, then at the same time submarines should no longer be melee units -- and a random-generator would have to be installed for the destroyers >> whether they can discover a sub or can sometimes not; and as well for the naval bombers.
But does anyone really want that in this game? I Think it is better so as it is now.
It seemed like such a waste to destroy an entire battle station just to eliminate one man. But Charlie knew that it was the only way to ensure the absolute and total destruction of Quasi-duck, once and for all.