The first inquest into the death of soldier Private Cheryl James who died at Deepcut barracks in 1995 was "extremely limited and had flaws," Judge Peter Thornton QC said.
Pte James was undergoing initial training at Deepcut when she was found dead with a bullet wound between her right eye and the bridge of her nose.
The first inquest was completed less than a month after she died. An early assumption had been that she had taken her own life.
"Her rifle was not examined forensically. No fingerprints were taken from it. No gunshot residue tests were made," Judge Thornton said.
Only a limited number of witness statements were taken. Very few witnesses were called to give evidence, and it was not surprising that the scope of the inquest was "circumscribed", said the judge.
The then Surrey coroner concluded with an open verdict after saying he was not able to find that suicide was proved beyond reasonable doubt.
The parents of the soldier who was found dead from a single gunshot wound at Deepcut barracks in November 1995 said they were "delighted" to have a fresh inquest into her death.
But Mr and Mrs James said "a meaningful inquiry into Cheryl's death is almost 20 years late."
The High Court has ordered a fresh inquest into the death of soldier Private Cheryl James who died at Deepcut barracks after a challenge by her family.
Mr Justice Mitting and Judge Peter Thornton QC both agreed that there was "an insufficiency of inquiry" at the 1995 inquest and quashed its open verdict.
Pte James, 18, was found dead from a single gunshot wound in November 1995.
Judge Thornton said "the discovery of new facts or evidence" made "a fresh investigation including a fresh inquest necessary or desirable in the interests of justice".
Pte James was one of four soldiers who died at the Surrey barracks between 1995 and 2002 amid claims of bullying and abuse. Privates Sean Benton, James Collinson and Geoff Gray also died from gunshot wounds.
The High Court has ordered a fresh inquest into the death of soldier Pte Cheryl James who died at Deepcut barracks after a challenge by her family.
The father of Private Cheryl James who died at Deepcut barracks, hopes his daughters death will be fully investigated if a new inquest takes place.
Des James says they may never know what happened to his daughter but her death must be investigated further.
Pte James was found dead after an apparent suicide in 1995. She was one of four soldiers who died at the barracks between 1995 and 2002.
The solicitor acting on behalf of the family, Emma Norton, says there is no guarantee that another inquest will take place.
Private James Collinson
Aged 17, from Perth, Scotland. Pte Collinson was found with a single gunshot wound through his chin in March 2002.
Private Cheryl James
Age 18, from Llangollen, north Wales. Pte James was found dead with a bullet through her forehead, in November 1995.
Private Sean Benton
Aged 20, from Hastings in East Sussex. Pte Benton was found dead with five gunshot wounds while on guard in June 1995.
Private Geoff Gray
Aged 17, from Seaham in County Durham. Pte Gray was found dead with two gunshot wounds to his head while on guard duty in September 2001.
The family of Cheryl James say they are relieved at the Attorney General's decision to allow them permission to apply for a fresh inquest into the death of their daughter.
Pte James was one of four soldiers who died at Deepcut barracks in Surrey between 1995 and 2002.
A Ministry of Defence spokeswoman said: "Our thoughts remain with the family and friends of Private Cheryl James.
"This decision is a matter for the Attorney General and the courts. "If a new inquest is ordered, we will of course provide support to the coroner when needed."