A decorated veteran was shot dead by a short-sighted soldier who had not put his glasses on.
The blunder which claimed the life of married dad Gavin Hillier, 35, happened at night on a rifle range.
A report found Sgt Hillier, 35, of 1st Battalion Welsh Guards, died almost instantly when he was hit by a squaddie who meant to fire at a wooden target.
The gunman did not have the specs he was meant to be wearing before he opened fire on March 1 last year.
Relatives of Sgt Hillier, a dad of two, said they were “absolutely devastated”.
The shooter is not being identified and is referred to as Guardsman 1. A police investigation is ongoing.
MoD bosses spent eight months probing the death of Sgt Hillier, who had received a long service and good conduct medal from Prince Charles, the Colonel of the Regiment.
The report found the shooter’s vision was so poor he was initially refused entry into the Welsh Guards. He was allowed to join only after being issued with corrective lenses and re-assessed.
But medical confidence rules meant Army medics could not inform the soldier’s chain of command that he needed to wear glasses. Instead it was the guardsman’s responsibility.
Sgt Hillier was acting as a safety supervisor when he was shot at Castle-martin training range, Pembrokeshire. He was wearing a yellow hi-vis jacket and a red chemical light stick was strapped to the back of his helmet.
But the report found the guardsman’s eyesight “meant that, to see the same level of detail as a normally sighted person, he would need to be three times closer if using both eyes or six times closer using just their right eye.
“Guardsman 1 was not wearing his corrective lenses and so his binocular vision would have seen Sgt Hillier, who was 143m away, in the same level of detail as someone with normal vision would have seen him at 429m. With their right eye (used to aim and fire) this would have increased to 858m.”
The soldier who fired the fatal shot had served just 18 months.
Sgt Hillier was a veteran of Iraq, Afghanistan and Kosovo and was in the job almost 20 years.
The report found 14 factors leading to Sgt Hillier’s death and made 20 recommendations.
Sgt Hillier’ widow Karyn and sons Declan and Connor said: “We are absolutely heartbroken and can’t express how proud we are of you. Our boys will continue to make you proud and you will forever live on through them.
“Daddy, we are not ready to say goodbye just yet so until we meet again, we love you always. Love, your heartbroken wife and boys.”
An Army spokesman said: “Our thoughts and sympathies remain with family and friends. We are supporting the investigation being led by Dyfed-Powys Police so it would be inappropriate to comment further.”