Taken word for word this card appears wrong, if you have to discard the card before deploying ships but place the mines beyond distance 5 of enemy ships. How do you place the mines before deploying if the have to be beyond distance 5 of enemy ships?
I assume nothing generally with cards but all I can guess is the intent is to...
1. Declare your intention to place proximity mine's before deploying ships.
2. Deploy fleets.
3. Place proximity mine's.
The problem is the card isn't explicit, my feeling is this card needs a clarification on the order of operations.