This dataset consists of measurements of underway meteorology, navigation and sea surface hydrography, sound velocity profiles, gravimetrics, swath bathymetry and seismic activity in the Mid-Atlantic Ridge. Data were collected by RRS James Cook cruises JC102 (06 - 18 April 2014), JC109 (011 October to 05 November 2014) and JC132 (14 January to 24 February 2016). The data were collected in the Mid-Atlantic Ridge as part of an investigation into the role and extent of detachment faulting at slow-spreading mid-ocean ridges. Sound velocity profiles were created using a Valdeport midas sound probe deployed once on each cruise. Gravity data were collected using a Lacoste_Romberg air-sea gravimeter. Navigation data were collected using an Applanix POSMV system and meteorology and sea surface hydrography were collected using the NMF Surfmet system. Both systems were run through the duration of the cruises, excepting times for cleaning, entering and leaving port, and while alongside. Swath bathymetry data were collected using a Kongsberg EM-120 multibeam echosounder, which was run throughout the duration of each cruise. These cruises formed the field component of NERC Standard Grant project "Role and extent of detachment faulting at slow-spreading mid-ocean ridges". Data were collected with the aim to determine (1) the sub-surface geometry and extent of the detachments beneath the ridge axis, (2) the amount and detailed distribution of magmatic crust, and (3) the asymmetry of spreading rates associated with oceanic core complexes and the volcanic seafloor. The Discovery Science project was composed of Standard Grant reference NE/J022551/1 as the lead grant with child grants NE/J02029X/1, NE/J021741/1. The lead grant, NE/J022551/1, ran from 01 April 2013 to 31 December 2019, and was led by Professor Timothy Reston, University of Birmingham, School of Geography, Earth and Environmental Sciences. Child grant NE/J02029X/1 ran from 01 March 2014 to 31 January 2019 and was led by Professor Christine Peirce, Durham University, Earth Sciences. Finally, child grant NE/J021741/1 ran from 01 January 2014 to 31 December 2018 and was led by Professor Christopher John MacLeod, Cardiff University, School of Earth and Ocean Sciences. All data have been received by BODC as raw files from the RRS James Cook. Underway navigation, meteorology and sea surface hydrography from JC132 and JC102 have been processed using BODC's in-house procedures and are available online. JC109 underway and sound velocity data for all cruises will be processed and made available online in the near future. Remaining data have been archived and are available as raw files on request.