Trainee officers at the Australian Defence Force Academy in Canberra will not be able to leave base until July 29.
The lockdown was implemented to coincide with the start of semester two on Monday.
Returning trainee officers include individuals from Victoria.
Individuals from Victoria who arrived after 12.01 am on Wednesday, July 8 are in mandatory quarantine for 14 days - in line with ACT government protocols.
An ADFA spokesperson said: "Those returning from Victoria have been accommodated separately to other Australian Defence Force personnel."
As a further precaution all other trainee officers are confined to the ADFA campus to further reduce the risk of transmission in the wider community.
"This is a precautionary measure only. There are no confirmed or suspected COVID-19 cases amongst ADFA trainee officers or staff," the spokesperson said.
"ADFA will continue to be advised by Defence's joint health command on testing and isolating of any possible COVID-19 cases."
The lockdown ends at 6pm on Wednesday, July 29.
"Defence is committed to ensuring the safety and wellbeing of all its personnel and the communities in which its personnel live and work," the spokesperson said.
"Comprehensive pastoral care and support is in place for the trainee officers while they are confined to campus, including meals being provided by the academy cadet mess."
