Two patients on Sark were taken to hospital in Guernsey by the ambulance boat on Saturday.
Mark Mapp, chief executive of Guernsey's Ambulance and Rescue Service, said at 16:30 BST the Sark doctor had requested Flying Christine III to urgently transport a patient with a medical condition to Guernsey.
He said shortly after the boat left St Peter Port the crew were told a second person had suffered a traumatic injury and also needed to be transferred to hospital.
It was the first medical mission of the year for the newly refurbished marine ambulance, Mr Mapp added.
Flying Christine III docked at St Peter Port at about 18:20, Mr Mapp said, from where the two patients were taken to the emergency department of the Princess Elizabeth Hospital by ambulance.
Earlier in the day the ambulance boat had been deployed to Sark to provide additional medical cover during the Princess Royal's visit for the island's 80th Liberation Day.
Mr Mapp thanked the volunteer boat crew who responded to the medical incidents and those who had manned the vessel during the royal visit.