A lack of direction and weak leadership has led to longstanding poor performance by the Welsh Ambulance Service, a report has concluded.
The trust bought 46 ambulances which were not fully fit-for-purpose
Auditor General Jeremy Colman has published an official inquiry into the "crisis-ridden" service
It follows a period which has seen response times worsen, and five different bosses over the last year.
It highlighted serious problems over years but also found "important strengths" providing optimism.
The audit report was commissioned by assembly members after an interim Welsh Ambulance Service chief executive quit, claiming the NHS trust was "in crisis" and its failures were putting lives at risk.
The service saw three chief executives over a three-month period - the latest, Alan Murray, has vowed to improve the service by the end of the year.
Last week, NHS statistics revealed that between July and September, just 54% of ambulances had reached an eight-minute target to respond to the most serious cases.
The figure was a fall from 57% recorded in the previous quarter and well below the assembly government's 60% target.
Referring to serious problems which had continued at the ambulance trust for several years, the auditor general's report pointed to a longstanding lack of direction as well as weaknesses in leadership at board level.
Inflexible shift patterns for ambulance crews had led to the service not matching the peak demands on ambulances and patient-care services, even though the overall staff and revenue resources appeared adequate.
Management failures had left the service with an inadequate fleet of ambulances, partly because it had a fleet of 46 vehicles which were not fully fit for purpose.
The auditor general also stated that more money would be needed to invest in a satellite navigation system and other computer software.
The report made 28 recommendations but noted the trust's "key strengths" - that it had enough staff and money to run its day-to-day operations and was in a position similar to other ambulance services that had gone on to improve themselves.
The report paid tribute to highly-skilled front-line staff
Mr Colman said: "It will take time to deliver sustained improvement but I am hopeful that the service can turn itself around as long as it addresses key challenges."
The report was welcomed by Mr Murray who said: "While the report has rightly pinpointed some long-standing problems, I wholeheartedly agree with its conclusion that we should be optimistic about the future of the service.
"There is a genuine passion and desire among our staff, whether they are people in green suits or people in grey suits, to improve the service.
"This is not a new situation for me. When I was brought in to help the Merseyside ambulance service, it was labelled as being the worst in England."
"But it was not a lost cause, far from it. Within a year, we managed to turn things round completely.
Welsh Health Minister Brian Gibbons, who inadvertently voted with opposition AMs who were calling for the inquiry, said: "I will be looking carefully at the report and considering where we need to focus our attention.
"We have already given our commitment to modernising the ambulance service in Wales and we are now working closely with the ambulance trust to take this forward."
Liberal Democrat health spokesperson Jenny Randerson said: "It took the combined opposition parties and the health minister's clumsy fingers to make it happen.
Plaid Cymru's health minister, Helen Mary Jones AM, said: "The report quite rightly identifies front-line ambulance staff as one of the strengths of the service.
"We now need to ensure that the further capital investment needed by the service, as identified in the report, is put in place alongside better capital planning to develop the service."
Welsh Tories health spokesman Jonathan Morgan AM said the blame for the service's shortcomings "lies with the way in which the service has been run since it was reformed in 1998 and also with the assembly government which is principally responsible for strategic direction and leadership".