Recently "Sentry" was used to help take 5,800 mass spectrometer readings in the sea at the site of the Deepwater Horizon explosion and subsequentoil spill in the Gulf of Mexico. It was sent 19 times into the under-water oil plume to provide data, using the TETHYS and CTD sensors, giving information on the chemical make-up and the positions of the plume. Detection was made as low as 50 micrograms per litre.