A ring assembly of an underwater acoustic sensor (hydrophone) system includes a ring that has brackets that mount the hydrophones evenly circumferentially spaced apart. The ring assembly may have three hydrophones mounted on the ring, with the hydrophones maintained in a triplet configuration. Multiple ring assemblies may be stacked in a nested array, with the hydrophones of adjacent stacked ring assemblies offset circumferentially, with each of the hydrophones overlapping multiple of the stacked rings, with the stacking accomplished such that the ring assemblies are in a helical array. Rings with non-acoustic sensors may be stacked with (and interspersed within) the stacked rings. The stacked array of ring assemblies (and non-acoustic sensor assemblies) may be stored in a canister that facilitates uniform and controlled descent and deployment of the assemblies, with ring assemblies and non-acoustic assemblies paying out sequentially from a float at the top of the array.