The "vast majority" of the military has been asked to follow Government-issued guidance on social distancing, home-working, and non-essential travel.
A letter sent to all Ministry of Defence staff from Chief of the Defence Staff (CDS) General Sir Nick Carter and Permanent Secretary Sir Stephen Lovegrove said: "For those of us not involved in the Coronavirus response and other essential defence activity, the need for exceptional measures applies equally to defence."
They encouraged leaders to think creatively about how they can "prioritise" business to make home-working possible, which could include work being delayed or stopped.
The letter outlines that essential output will continue.
Anyone delivering "non-discretionary operations or those which are vital to sustaining the defence enterprise over the next six months" should continue to work as usual.
A responsible officers has been appointed to help oversee the risks home-working may cause to the delivery of defence outputs.
They will also be working across defence to understand the effect coronavirus is having on business and will issue more detailed guidance and advice on managing these risks over time.
The Government has also identified military personnel as key workers.
The letter offers guidance to personnel, stating that those "critical to delivering essential outputs" will be quickly identified.
"Designating 'key workers' from across a large workforce is an inherently difficult and potentially awkward task.
"We need to keep the number as low as possible.
"It will not be about seniority."
In regards to how long personnel will be expected to prioritise home-working, the letter says: "This will last until teams are required to exit self-isolation to support the coronavirus response or essential operations, or the Government advice changes".
The letter is signed off with a message from both the CDS and Permanent Secretary, saying: "We have confidence that throughout defence we have the strong leaders we need to see us through the challenges ahead."