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Pentamode (PM) materials are degenerated elastic solids only supporting one state of stress, which is not necessarily hydrostatic. Inviscid fluids can be considered as natural isotropic PM materials, while a general PM material is able to support off-axis shear. This peculiar property makes them very promising in underwater acoustic wave control, particularly with the advance of transformation acoustics theory. These materials can be made approximately from conventional solids with careful microstructure design. In this talk, we will first present a design method for Pentamode materials which are impedance matched with water. Then a pentamode acoustic cloak is designed with transformation theory and is constructed with the proposed latticed pentamode materials. Finally the performance of the underwater cloak is examined experimentally in a special designed water wave guide, demonstrating the expected broadband property. The finding paves the way for controlling underwater acoustics using broadband solid metamaterials.