compound indicated by numeral 28 on fig1 while it is envisaged that adequate interlocking will be achieved simply by virtue of the weight of each section it may be additionally desirable prticularly as between sections 10 and 17 to provide separate anchoring means such as hydraulic bolts should it become essential to affect the release of section 17 from the base 10 such bolts could be provided with explosive heads remotely actuated from the elevated deck an additional feature of this invention would be to dimension base 10 to include oil or liquid natural gas storage chambers and to adapt the deck 19 to facilitate mooring and the transferral of oil or l n g to a surface vessel in the embodiment discussed heretofore the third upper section 18 is exemplified by a composite structure comprising an operating platform 19 and a sole vertical supporting column 20 the column being initially carried by the platform and adapted to be lowered into operable engagement with the second conical section 17 and utilized subsequently to raise the platform to its operating height it is however within the scope of the present invention to include the supporting column as in integral part of section 17 in the manner shown schematically in fig7 here column 20 is an extensible component of section 17 slidably contained within the section in a telescopic fashion following submergence and coupling of section 17 to base section 10 column 20 is telescopically extended until its upper end 20 c engages and is locked with the floating platform 10 continued extension of column 20.