In an email obtained by News Limited newspapers, the soldier claims digger Jared Mackinney would be alive if troops had been given adequate fire support and better intelligence.
The soldier said it was a miracle five or six more Australians had not been killed during the battle of Derapet on August 24.
He said the army had exposed troops to unnecessary risks.
"That contact would have been over before Jared died if they gave us f.....g mortars," the soldier said in his email.
It also detailed how no intelligence reports had prepared the two sections of about 24 men each for a confrontation with up to 100 enemy attacking from multiple firing positions as close as 80m away.
"We were at times pinned down by a massive rate of fire but we stuck to it," he wrote.
"The army has let us down mate and I am disgusted."
