Geophysical and underway data collected along the Louisville Ridge-Tonga Trench. Cruise SO215 (April to June 2011) dataset https://portal.medin.org.uk/portal/start.php?tpc=006_983ac9624b0b59ce89549e05ff05ac39 This dataset consists of measurements of underway meteorology, navigation and sea surface hydrography, seismic reflection and refraction, and bathythermograph data collected during a comprehensive survey of the Tonga-Kermadec island arc-deep-sea trench system, undertaken between April and June 2011. Data were collected on RV Sonne cruise SO215 by an integrated marine geophysical experiment that comprised simultaneous seismic reflection (MCS) and wide-angle (WA) refraction, gravity, magnetic, bathymetry and sub-seabed high-resolution imaging of the Louisville Ridge-Tonga-Kermadec Trench collision system. This cruise formed the field component of NERC Discovery Science project "The Louisville Ridge-Tonga Trench collision: Implications for subduction zone dynamics". The key scientific objectives for the cruise were as follows: a) Determine the 'background' crustal and uppermost mantle structure of the subducting plate; b) Determine the crustal and uppermost mantle structure across and along the Louisville Ridge; c) Determine the physical properties of the leading edges of the subducting and over-riding plates; d) Determine the state of isostasy, ridge-related flexure and moat characteristics at the Louisville Ridge, and the mechanical properties of the subducting and over-riding plates; e) Determine the seafloor morphology and collision-related deformation in the Tonga forearc. The Discovery Science project was composed of Standard Grant reference NE/F004273/1 as the lead grant with child grant NE/F005318/1. The lead grant ran from 01 Mar 2011 - 31 Aug 2016 and the child grant ran from 01 Oct 2010 - 30 Sep 2014. Professor Christine Peirce of University of Durham, Department of Earth Sciences was the principal investigator of the lead grant of this project. Prof Anthony Watts of University of Oxford, Earth Science was the principal investigator of the child grant. The bathythermograph data have been received by BODC as raw files from the RV Sonne, processed and quality controlled using in-house BODC procedures and will be made available online soon. The remaining data have been received by BODC as raw files from the RV Sonne and are available on request. 20180518 20231206