Navies have been operating with unmanned underwater vehicles (UUVs) for decades. Recently, these platforms are assigned more and more complicated tasks. Compared to other domains, the underwater domain offers substantial additional challenges. One of these challenges is accurate navigation of these UUVs. In this thesis, the use of directional acoustic modems integrated onto autonomous platforms is evaluated, specifically in the role they can play in improving underwater navigation accuracy of submerged assets. The main research effort within this thesis was the evaluation of data from sea trials in the shallow parts of Monterey Bay in September 2017 and April 2018. Two directional acoustic modems were installed in tow bodies that were tethered to two unmanned surface vehicles (USVs). These USVs were then directed on multiple missions in an area surrounding the deployment of a bottom-moored acoustic echo repeater, which acted as a surrogate underwater platform. Data collected during the sea trials is then compared between measured and best-estimated ranges and bearings. Using the Bellhop ray-tracing model and beam pattern analysis, the actual accuracy of these systems was extensively evaluated. Results indicate that, when operating properly, these modems can provide accurate data to assist in underwater navigation.http://archive.org/details/evaluatingeffect1094559609Outstanding ThesisLieutenant, Netherlands NavyApproved for public release; distribution is unlimited.