"The military commission system is transparent all right – transparently corrupt," Terry Hicks said, exuberant about the leniency of his son's sentence but still furious about the treatment the 31-year-old Muslim convert has endured for five years.

David Hicks will serve a nine-month sentence in a prison in his hometown of Adelaide after admitting last week that he aided al-Qaida in a plea deal at the US naval base at Guantanamo Bay.

The deal prevents him from talking to the media for 12 months or pursuing his allegations of abuse while in US custody.

Legal observers and opposition lawmakers have joined Terry Hicks in saying the deal is tailored to remove potential political embarrassment for Australian Prime Minister John Howard, who will seek his fifth three-year term as national leader at elections due later this year.