This paper presents a novel algorithm for determining the 3D location of a Mobile Tag (MT) using wireless Base Stations (BSs) and Ultra Wide Band (UWB) one-way signaling. The algorithm is designed for low power, rapid deployment applications in which the BSs are independent, wireless UWB transceivers located at known positions and the tags are receive-only or transmit-only UWB mobile units. The algorithm utilizes multi-BS time synchronization and hybrid Time Difference of Arrival-Time of Flight (TDoA-ToF) localization to achieve high accuracy tag localization. The algorithm consists of two concurrent tasks. In task I, the BSs exploit periodic inter-BS transmissions to obtain high accuracy multi-BS time synchronization. In task II, a hybrid TDOA-TOF algorithm is used to determine the location of the MT. The algorithm is based on timestamping, or control, of packet Time of Emission (ToE) and estimation of the packet Time of Arrival (ToA). As such, the method is appropriate for use with, but not limited to, IEEE 802.15.4a UWB. In simulations assuming a typical 2 cm standard deviation in ToA estimation error the proposed algorithm was found to provide a RMS error of 2.1 ps and 4.8*10^-6 ppm for time offset and crystal clock offset between BSs respectively; and a RMS error in MT location estimation of 2.2 cm; which is 36% better accuracy than the conventional TDoA method.