Smoothing algorithms for maneuvering target tracking with nonlinear target dynamic and measurement equations are described and investigated. Target motion is represented using a multiple model approach. Techniques based on the interacting multiple model filter (IMMF), hypothesis pruning and maximum a posteriori (MAP) estimation of the maneuvering mode are described. All three techniques are based on the use of the unscented transformation with an augmented state model. A procedure for selecting the sigma points which exploits the partial lineairty of the augmented state model is used. The performances of the algorithms are analysed using a scenario involving a target which undergoes coordinated turn maneuvers. In this scenario, for a sufficiently large number of smoothing lags, the MAP approach and the pruning algorithm have almost equal performance and significantly superior performance to the augmented state IMMF. The MAP approach has the benefit of a reduced computational expense