As hospitals across the south continue to deal with increasing pressure, the army has arrived at the Royal Sussex County Hospital in Brighton to help ambulance crews.
Paramedics and call handlers at South Central and South East Coast Ambulance services are among those taking part in a national strike in an ongoing dispute over pay and conditions.
About 600 members of the Army, Navy and RAF from across the country have been drafted in to help during the walkouts, some of whom have never driven the vehicles before.
They've been deployed to try and help relieve some of the pressure on the NHS Trusts from staff sickness and increased demand.
Five hospital trusts across the region have declared a system-wide critical incident this week, including South East Coast Ambulance Service. The service said it comes "following a period of more than a week of sustained pressure across our 999 and 111 services, significantly impacting on our ability to respond to patients".
The NHS in Sussex has issued advice for patients and the public during ambulance industrial action.
A spokesperson for the Integrated Care Service said: "Regardless of any strike action taking place, patients who need urgent medical care will be prioritised, especially in emergency and life-threatening cases – when someone is seriously ill or injured, or their life is at risk.
"On days where there is strike action, you should only call 999 if it is a medical or mental health emergency (when someone is seriously ill or injured and their life is at risk).
"Ambulances will still be able to respond in these situations, but this may only be where there is an immediate risk to life.
"There will be fewer ambulances on the roads during the industrial action and it is likely 999 call handlers will be very busy, but the NHS will be prioritising those with life-threatening needs.
"As a result patients whose conditions are not life-threatening are likely to have very long waits for an ambulance on strike days."
Members of the armed forces taking part in the two days of training at the barracks said they were “nervous” but “honoured” to cover for ambulance workers, despite having to sacrifice time off.Personnel covering for striking ambulance workers on Wednesday will not be allowed to break red lights or turn on blue lights when driving.
They are not due to be sent on critical emergency callouts or carry out clinical tasks but ambulance trainers have told them they should be prepared to hand equipment to their clinical partner if asked.