This dataset describes an evaluation project using ocean glider data collected in the Celtic Sea, funded by the United Kingdom Integrated Marine Observing Network (UK-IMON) initiative. The data measured form a three dimensional trajectory through the water column covering a transect from just North West of the Scilly Isles, to the South west in the Celtic Sea. The date span for the data is 12 September 2013 to mid-October 2013 (expected). Deployment occurred off the RV Cefas Endeavour on 12th September and it is expected that the gliders will be recovered in Mid October. The project includes 2 ocean gliders, both equipped with a CTD and triplet optical phytoplankton fluorescence, backscatter and coloured dissolved organic matter sensor. There is also an echo sounder (on one glider) and Sea Mammal Research Unit (SMRU) Passive Acoustic Monitor (PAM) (cetacean monitoring) on the other glider. The goal of the evaluation project is to study tidal mixing and to contribute to oceanographic sensor development. The organisations contributing to the dataset are the UK National Oceanography Centre (NOC), the Centre for Environment, Fisheries & Aquaculture Science (CEFAS) and the Sea Mammal Research Unit (SMRU). The data are held by BODC as an archive of the real time data stream as transmitted by the glider. The delayed mode full resolution (downloaded on platform recovery) and delayed mode quality controlled data are expected in due course.