Apparatus for use in the investigation and analysis of an underwater floor of a body of water, the apparatus comprising: a seabed platform which in use is disposed on the underwater floor; a depth penetration device which comprises a drillstring; an underwater floor testing tool (10, 11, 12, 15) which in use is received within a borehole in the underwater floor; and a probe assembly which in use is received within the borehole in the underwater floor, comprising: a first coupling for operatively connecting the probe assembly to the depth penetration device; a second coupling for operatively connecting the probe assembly to the underwater floor testing tool (10, 11, 12, 15); and a plurality of modules (2, 3, 5) which in use are assembled together and configured so that the plurality of modules (2, 3, 5) can be received within the borehole, the plurality of modules (2, 3, 5) including a signal processing module for processing information received from the underwater floor testing tool (10, 11, 12, 15), a data transmission module for the wireless transmission of data from the signal processing module through the drillstring to the seabed platform, and a power source module for powering the data transmission module, the signal processing module and the underwater floor testing tool (10, 11, 12, 15), the apparatus being characterized in that the plurality of modules (2, 3, 5) further comprising a switch module which includes a magnetically responsive switch device, arranged to electrically connect and disconnect the power source module to the data transmission module, the signal processing module and the underwater floor testing tool (10, 11, 12, 15) when the magnetically responsive switch device is in the vicinity of a magnetic field, by the magnetically responsive switch device changing from a normally closed state to an open state. a seabed platform which in use is disposed on the underwater floor; a depth penetration device which comprises a drillstring; an underwater floor testing tool (10, 11, 12, 15) which in use is received within a borehole in the underwater floor; and a probe assembly which in use is received within the borehole in the underwater floor, comprising: a first coupling for operatively connecting the probe assembly to the depth penetration device; a second coupling for operatively connecting the probe assembly to the underwater floor testing tool (10, 11, 12, 15); and a first coupling for operatively connecting the probe assembly to the depth penetration device; a second coupling for operatively connecting the probe assembly to the underwater floor testing tool (10, 11, 12, 15); and a plurality of modules (2, 3, 5) which in use are assembled together and configured so that the plurality of modules (2, 3, 5) can be received within the borehole, the plurality of modules (2, 3, 5) including a signal processing module for processing information received from the underwater floor testing tool (10, 11, 12, 15), a data transmission module for the wireless transmission of data from the signal processing module through the drillstring to the seabed platform, and a power source module for powering the data transmission module, the signal processing module and the underwater floor testing tool (10, 11, 12, 15), the apparatus being characterized in that the plurality of modules (2, 3, 5) further comprising a switch module which includes a magnetically responsive switch device, arranged to electrically connect and disconnect the power source module to the data transmission module, the signal processing module and the underwater floor testing tool (10, 11, 12, 15) when the magnetically responsive switch device is in the vicinity of a magnetic field, by the magnetically responsive switch device changing from a normally closed state to an open state.