The coastguard has been drafted in to support an ambulance service hit by high levels of Covid-19 patients.
Two coastguard vehicles will be able to attend non-Covid patients in Suffolk and north east Essex if requested by the East of England Ambulance Service.
The volunteers will be community first responders who will attend an emergency before ambulance staff.
Claire Hughes, from HM Coastguard, said it was to "help reduce the pressures on the NHS" due to Covid-19.
The vehicles will operate from Colchester, Essex, and Saxmundham, Suffolk, and each will carry two volunteers.
Eleven volunteers from Aldeburgh, Felixstowe, Shingle Street, South Woodham Ferrers, Southend, West Mersea and Lowestoft coastguard teams were trained last week by a specialist paramedic and community first responder.
Jeremy Littlewood, senior coastal operations officer for HM Coastguard in the South East, said: "We are proud of our volunteers for the professionalism and commitment they have shown throughout the training sessions."
The support is due to run until the end of the month but the agreement could be extended depending on the requirements of the NHS.
Essex had some of the highest Covid-19 infection rates in the country over the past month and has four areas in England's top 20 for case rates.
Last week, Southend Hospital's oxygen supply "reached a critical situation" due to rising numbers of coronavirus infections.