The Defence Force is struggling to get skilled personnel and has spent $20 million on advertising to attract new recruits in the past three years.
It plans to spend nearly $15 million in the next three years.
Commander Nigel Philpott says military personnel are required to do extremely technical work in very challenging environments.
He says it's particularly hard to find people skilled in trades critical for operational deployments such as engineering, technicians and medicine.
Commander Philpott says advertising is unavoidable but Defence has managed to spend less on it.