A method of retrieving a mobile platform from a tank having a hatch and at least partially filled with a non-conductive, energetic substance (12, 14), the method characterized by: - configuring the mobile platform to include at least: - an enclosure, - at least one control unit positioned inside the enclosure, - at least one propulsion system positioned at least partially inside the enclosure, - at least one power supply positioned inside the enclosure, and - at least one retrieval system disposed at least partially on the enclosure and including at least: - at least one buoyant body, - at least one primary tether connected to the at least one buoyant body and to the enclosure; - at least one secondary tether connected to the at least one buoyant body and to the enclosure; - predetermining a buoyant body retrieval zone within the tank, wherein the buoyant body retrieval zone is below the hatch; - lowering the mobile platform into the tank using a deployment carrier (50, 764, 780); - submerging the enclosure in a non-conductive, liquid energetic substance; - moving the mobile platform using the at least one propulsion system to perform at least one task in the tank; - releasing the at least one buoyant body and the at least one primary tether from the enclosure; - positioning the released at least one buoyant body within the buoyant body retrieval zone by using the at least one primary tether; - accessing the at least one buoyant body through the hatch; - retrieving the at least one primary tether by using the at least one buoyant body; - using the at least one primary tether to release the at least one secondary tether; and - inserting a retrieval member through the hatch to retrieve at least one of: (i) the at least one buoyant body, (ii) the at least one primary tether, and (iii) the at least one secondary tether. - configuring the mobile platform to include at least: - an enclosure, - at least one control unit positioned inside the enclosure, - at least one propulsion system positioned at least partially inside the enclosure, - at least one power supply positioned inside the enclosure, and - at least one retrieval system disposed at least partially on the enclosure and including at least: - at least one buoyant body, - at least one primary tether connected to the at least one buoyant body and to the enclosure; - at least one secondary tether connected to the at least one buoyant body and to the enclosure; - an enclosure, - at least one control unit positioned inside the enclosure, - at least one propulsion system positioned at least partially inside the enclosure, - at least one power supply positioned inside the enclosure, and - at least one retrieval system disposed at least partially on the enclosure and including at least: - at least one buoyant body, - at least one primary tether connected to the at least one buoyant body and to the enclosure; - at least one secondary tether connected to the at least one buoyant body and to the enclosure; - at least one buoyant body, - at least one primary tether connected to the at least one buoyant body and to the enclosure; - at least one secondary tether connected to the at least one buoyant body and to the enclosure; - predetermining a buoyant body retrieval zone within the tank, wherein the buoyant body retrieval zone is below the hatch; - lowering the mobile platform into the tank using a deployment carrier (50, 764, 780); - submerging the enclosure in a non-conductive, liquid energetic substance; - moving the mobile platform using the at least one propulsion system to perform at least one task in the tank; - releasing the at least one buoyant body and the at least one primary tether from the enclosure; - positioning the released at least one buoyant body within the buoyant body retrieval zone by using the at least one primary tether; - accessing the at least one buoyant body through the hatch; - retrieving the at least one primary tether by using the at least one buoyant body; - using the at least one primary tether to release the at least one secondary tether; and - inserting a retrieval member through the hatch to retrieve at least one of: (i) the at least one buoyant body, (ii) the at least one primary tether, and (iii) the at least one secondary tether.