TROIKA PLUS: This system employs up to four remote controlled Seehund (sea dog or seal) drones which perform the sweep. The drones are small unmanned boats that can simulate the acoustic and magnetic signatures of bigger ships to trigger mines. Their small size and special construction let them survive the effects of exploding mines unharmed. Seehund can be controlled remotely or manually by an onboard crew (usually 3) for maneuvering in harbours or in training (the Seehund is too large to be carried by Ensdorf class vessels). A life raft is carried for this reason.