With the ‘Lay Mines’ mission a ship will transform it’s torpedoes into mines. Different torpedo technologies can create a different number of Deep Space Mines. The most cost effective torpedo in terms of Megacredits for minelaying are the Mark 4 and Mark 7 Photon Torpedoes, while the Mark 8 is much more expensive in Megacredits but lower in the mineral use. For most players the Mark 7 is the only true technology for laying serious Minefields.