A method of making a tubular casing for an underwater device, in particular a torpedo, characterised in that it comprises the following steps: - preparing at least one metal ring comprising a tubular wall coaxial to an axis of symmetry; the tubular wall having, on the outside-facing surface, a first groove and a second groove spaced axially and radially with respect to the first groove; - subjecting said metal ring to an anodizing process that produces an insulating layer of oxide that covers the outer surfaces of the metal ring; - coupling said ring with a mould that defines a cylindrical supporting surface coaxial to said axis; - depositing a plurality of first layers of fibre on the cylindrical portion of said mould and on a portion of said ring comprising said first groove to produce a first cylindrically-shaped tubular element in fibre provided with an end portion that engages said first groove; - depositing on said first tubular element in fibre at least one layer of syntactic or equivalent material configured to transfer radial forces; - depositing a plurality of second layers of fibre on the layer of syntactic material and on a portion of said ring comprising said second groove to produce a second cylindrically-shaped tubular element in fibre provided with an end portion that engages said second groove; said second tubular element in fibre housing the first tubular element in fibre and said layer of syntactic or equivalent material; - subjecting said first and second tubular elements to a heating cycle so as to perform polymerization of the fibre that adheres intimately with the layer of syntactic material producing said tubular casing in which a solidified portion of fibre is provided internally with an intermediate portion formed by the syntactic material and having an end portion that engages the first and the second groove; and - removing said mould from said tubular casing. - preparing at least one metal ring comprising a tubular wall coaxial to an axis of symmetry; the tubular wall having, on the outside-facing surface, a first groove and a second groove spaced axially and radially with respect to the first groove; - subjecting said metal ring to an anodizing process that produces an insulating layer of oxide that covers the outer surfaces of the metal ring; - coupling said ring with a mould that defines a cylindrical supporting surface coaxial to said axis; - depositing a plurality of first layers of fibre on the cylindrical portion of said mould and on a portion of said ring comprising said first groove to produce a first cylindrically-shaped tubular element in fibre provided with an end portion that engages said first groove; - depositing on said first tubular element in fibre at least one layer of syntactic or equivalent material configured to transfer radial forces; - depositing a plurality of second layers of fibre on the layer of syntactic material and on a portion of said ring comprising said second groove to produce a second cylindrically-shaped tubular element in fibre provided with an end portion that engages said second groove; said second tubular element in fibre housing the first tubular element in fibre and said layer of syntactic or equivalent material; - subjecting said first and second tubular elements to a heating cycle so as to perform polymerization of the fibre that adheres intimately with the layer of syntactic material producing said tubular casing in which a solidified portion of fibre is provided internally with an intermediate portion formed by the syntactic material and having an end portion that engages the first and the second groove; and - removing said mould from said tubular casing.