Michael Pikesley, 25, of Honiton, Devon, was sentenced at Exeter Crown Court after being convicted last month of inflicting grievous bodily harm with intent on the 16-month-old boy he was looking after.
Pikesley, a private, was jailed for six years for that offence with four months for breaching a two-year conditional discharge imposed for causing bodily harm when the child was six months.
Pikesley, who committed the latest offence after coming home on leave from Bosnia over Christmas 1993, sat with his head in his hands after sentence was passed. Judge Graham Neville said that on the latest occasion, Pikesley had pulled out two of the child's toenails "with something like a pair of pliers".
He added: "The only purpose of doing that was to inflict extreme pain on that baby." The child must have been in agony, the judge said.
Earlier, Richard Rains, for the defence, said a loss of temper was the only sensible explanation he could offer.
But the judge said: "That was not temper at all. That was sadism . . . I have got to protect children from sadism."
Pikesley's company commander, Major Brian Mather, said that Pikesley had joined up in 1986 and would be discharged from the Army if he received a custodial sentence.
During the trial, Pikesley claimed he had found the child with the nails hanging off and had removed them before bathing and bandaging them.