Here is a short overview of the mine laying system. First of all, there are 2 main types of mines: Drift mines and anchor mines. Here the big Drift mine could be seen. It can only be placed if you own the minelayer of the boat. You can lay this mine at a depth of 30 - 70 meters.
A second type mine is the smaller 533 mm mine that is ejected from the torpedo shaft. This fires like a torpedo, but it is much smaller, and does much less damage.
Further explanations of how this works are available in the Toturials. We'll stay with this mine: This mine is an "intermediate" between the Minecraft Boats (World War 1) and Seahunter Type VII C (World War II) and thus a game decision. Game decisions can be freely chosen (that is, nobody has to use them, you are welcome to use "only" the small ones). The advantage of this mine is that it has an explosive force of 500 kg. So it is a serious opponent. After releasing a mine, it will take some time (see picture) until the mine becomes sharp.
However, mines make no difference between friend and foe, and since this is not anchored here with a rope, it drives. She is a very good weapon against convoys, but no guarantee. Depending on how many torpedoes you take, you can invite 10 pieces of these (big) mines (but only 4 torpedoes). The use of mines in Seahunter should have been planned and considered carefully for a long time. I'll show you the strategy later when the gameplay videos start (that's a time factor since I'd like to comment on them). please be patient until then.
Mines, cleverly used, can be a fantastic defense for destroyers. However, the mine itself drives very slowly to the surface, so it is not a good "defense weapon", but intended for the explicit strategic use. There are 3 direct mine-missions in Seahunter.
And remember: once the mine is sharp, it makes no difference between friend and enemy anymore.