He was also found guilty of indecently assaulting a third recruit.
He was found not guilty on five charges relating to sexual violation and inducing a sexual connection by threat.
Judge Blackie said the sentence was to deter others from conducting themselves in the same way. "The policy on fraternisation is common knowledge and was a fundamental understanding of anyone in command, and you were in command."
Manning would groom female recruits with a view to making sexual advances for his own sexual gratification, Judge Blackie said.
"As new recruits you would have expected them to trust you, to look up to you, to obey you."
Earlier yesterday, the court was told Manning had been honoured for his actions during service in Afghanistan. Captain Mathew Marinovich, who spoke as a character witness, said the bombardier had served in Afghanistan and East Timor and performed to a "high standard".
Manning was awarded the Distinguished Service Decoration in the 2009 New Year Honours list for an incident in Afghanistan where he intervened and halted a violent altercation between two local police officers.
There is a 30-day period in which Manning can appeal.