What does the hydrostatic release unit (HRU) on a bracket-mounted EPIRB do?

A. It prevents the EPIRB from activating accidentally in heavy rain or spray

B. The HRU controls the EPIRB's transmission power based on water depth

C. It releases the EPIRB when a manual lanyard is pulled by a crew member

D. It automatically releases and activates the EPIRB when submerged to approximately 1.5–4 metres — if the vessel sinks, the EPIRB floats free and activates without any manual action required

A. To send a digitally coded distress alert containing the vessel's MMSI and position automatically to all DSC-equipped stations and the Coastguard

B. To broadcast weather forecasts to other vessels

C. To make telephone calls from the vessel to shore

D. To operate the radar system remotely

A. A GPS waypoint identifier used in coastal navigation

B. Maritime Mobile Service Identity — a unique 9-digit number identifying the vessel; without it a DSC distress alert cannot identify the vessel to rescuers

C. A VHF channel number allocated by Ofcom for distress use only

D. A vessel survey certificate number required by the MCA