An acoustic localization system using a linear hydrophone array is presented which has been designed to provide three dimensional positioning information relative to a signal source for testing in confined environments such as swimming pools or water tanks. The system is designed to fit within the size, power, and computational limitations of resource constrained small underwater vehicles. The feasibility of the technique was demonstrated in a confined test environment with severe multipath signals. Experimental test results in a 8 m diameter, 4.5 m deep steel tank show localization errors of less than 5% of the slant range which is comparable to commercially available systems designed for large vehicles in the open ocean.