The present work describes a method for estimating the acoustic target strength of a submarine with a model composed of several simple reflectors. For each such reflector an analytical solution, based on the theory of Fresnel zones is applied. The model is further enhanced by calculation of transmission through outer elements to inner, hidden reflectors. The target area of the submarine is calculated as the sum of all target areas of the parts. The model is part of Submarine Analysis (SubAn); An application toolbox supporting design activities in the early phases of a submarine design project. This is a revision and extension of the report FOI-R-3666-SE from 2013.