  KM3NeT is a research infrastructure being installed in the deep Mediterranean
Sea. It will house a neutrino telescope comprising hundreds of networked
moorings - detection units or strings equipped with optical instrumentation to
detect the Cherenkov radiation generated by charged particles from
neutrino-induced collisions in its vicinity. In comparison to moorings
typically used for oceanography, several key features of the KM3NeT string are
different: the instrumentation is contained in transparent and thus unprotected
glass spheres; two thin Dyneema ropes are used as strength members; and a thin
delicate backbone tube with fibre-optics and copper wires for data and power
transmission, respectively, runs along the full length of the mooring. Also,
compared to other neutrino telescopes such as ANTARES in the Mediterranean Sea
and GVD in Lake Baikal, the KM3NeT strings are more slender to minimise the
amount of material used for support of the optical sensors. Moreover, the rate
of deploying a large number of strings in a period of a few years is
unprecedented. For all these reasons, for the installation of the KM3NeT
strings, a custom-made, fast deployment method was designed. Despite the length
of several hundreds of metres, the slim design of the string allows it to be
compacted into a small, re-usable spherical launching vehicle instead of
deploying the mooring weight down from a surface vessel. After being lowered to
the seafloor, the string unfurls to its full length with the buoyant launching
vehicle rolling along the two ropes.The design of the vehicle, the loading with
a string, and its underwater self-unrolling are detailed in this paper.
