The change is meant to double the “contingent reserve” – the pool of former personnel who can be called upon in a crisis – to close to 20,000 people within the next five years.

A 2024 strategic review of the reserves warned that the existing reserve pool was too low and highlighted that training a soldier costs about $173,000 on average in the first twelve months.

By keeping more highly trained people linked to the Defence Force, the ADF hopes to get better value for that training investment, since the cost rises sharply as soldiers gain experience.

Under the new rule, former personnel will be placed in “service category two”. This is an unpaid contingency reserve; members have no regular training or service duties, but they must be ready to respond if they are called up.

Existing ADF members can opt‑in to the ten‑year commitment, while the ten‑year period automatically applies to anyone who joins after 1 October 2024.

Defence Minister Richard Marles said the move comes as recruitment numbers are improving and the Defence Force is “investing in our people” to meet future security needs.