Extra staff will help turn round the East Midlands Ambulance Service (EMAS) which scored badly in the health ratings, says a health union.
EMAS "significantly underachieves" despite an £11m investment
EMAS scored two stars out of a possible three last year but the rating has now fallen to one in the latest figures.
It was found to have "significantly underachieved" when answering serious, but non life-threatening calls.
Unions claim morale is at rock bottom, but support a management statement saying improvements have started.
Maurice Haslam, the UNISON branch secretary, said: "We received additional staff last year and additional staff this year, and by this time next year we will have another 100 operational staff within the service, which is a considerable investment.
"Obviously with that level of investment, and with the additional vehicles we will be able to employ, we are quite confident we will be achieving all of the Government's figures."
In a statement, EMAS chief executive Paul Phillips, said: "The award of one-star must be taken in context.
"The fact is we are only now in the second year of a three-year PCT investment programme that, over time, will enable us to hit the National targets."
Ambulance service star ratings 2005 (2004)
EMAS 1 (2)
LINCOLNSHIRE 2 (0)
TWO SHIRES-NORTHANTS 3 (3)
EMAS has an £11m investment plan and is still recruiting staff to bring its service up to scratch in a plan which started last year.
Its neighbouring services performed better in the 2005 ratings released on Wednesday.
The NHS rated all hospitals, ambulance services and primary care trusts nationally. No hospital or primary care trust in the EMAS area scored less than two stars.
Star ratings were introduced in 2001, but these are to be the last and are to be replaced with more general health checks for trusts which provide hospital, ambulance and GP services.