such as occurs during deep submergence operations conventional composite hull structures require a core material that must be rigid in through the thickness compression i e the core material must have compressive strength slightly higher than the maximum depth pressure to which the hull would be subjected in the improved hull structure disclosed herein the tubing lends an added resistance to hydrostatic loading that is not possible with conventional core material applications in effect the tubing provided in accordance with the present invention replaces a majority of the core material and serves to increase the maximum stress which can be sustained by a composite hull structure constructed in accordance with the present invention the maximum stress on the tubing will be a result of its internal fluid pressure and is dictated by the design depth pressure of the hull which is directly proportional to the diameter d of the tubing and inversely proportional to the thickness of the tubing side wall the relatively small diameter of the tubing enables these tubes to carry a fluid at full pressure with minimal tubing wall thickness a result which yields weight savings in the hull structure still with reference to the fig1 an annular fitting 4 is provided at the end of the generally cylindrical hull structure to either mate with an adjacent hull section or to receive a nose cone or tail cone of the submersible vessel not shown in order to provide fluid access to the tubing assembly shown in the figure plumbing fittings not shown would be provided either through the annular fitting 4 or instead might be provided through the inner skin 1 of the composite hull structure although such plumbing is not.