London's Air Ambulance, also known as London HEMS (Helicopter Emergency Medical Service), is a British registered charity that operates an air medical service dedicated to responding to serious trauma emergencies in and around London. Using a helicopter by day and road vehicles by night, it functions as a mobile emergency department in life-threatening, time-critical situations. London's Air Ambulance was founded in 1989 in response to a report by the Royal College of Surgeons which documented cases of patients dying unnecessarily because of the delay in receiving prompt and appropriate medical care. The charity was the first in the UK to carry a senior doctor in addition to a paramedic at all times on a helicopter, introducing a system that reduces the death rate in severe trauma by 30–40%.