Do what BB just said. You do that, and all your mines will be placed into the same feild. REMOTE DEPLOY mines works great for that. Remember that you can only deploy mines equal to your minelayers on your ship. So if you have only 5 minelayers on your ship, thats all the mines you can deploy from that ship at one time. Good luck, and mine away.
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"We've made too many compromises already, too many retreats! They invade our space and we fall back -- they assimilate entire worlds and we fall back! Not again! The line must be drawn here -- this far, no further! And I will make them pay for what they've done!" -- Patric Stewart as Captain Picard
UCP/TCO Ship Yards