Up to 3,000 armed forces reservists are being called up to aid the military response to the coronavirus pandemic.
Individuals with specialist skills will provide medical and logistical support to the NHS, engineers and accountants, the Ministry of Defence said.
The MoD said it had identified the units and individuals it will need and notified their employers.
Reserves who are already working in the NHS or delivering front-line services will not be called up.
The MoD has already set up a 20,000-strong Covid-19 response force to help in the fight against the virus, though only a few thousand full-time military personnel have so far been deployed.
They have been assisting in tasks such as delivering protective clothing to the NHS and building the Nightingale Hospital in east London, the first of several new temporary hospitals to be set up across the UK.
The hospital, being set up in London's ExCeL centre, is due to be operational this week, despite building work only starting last Wednesday.
The 4,000-bed facility will be split into more than 80 wards containing 42 beds each and will be one of the biggest hospitals in the world, according to its chief operating officer, Natalie Forrest.
The facility will be used to treat Covid-19 patients who have been transferred from other intensive care units across London.
A further two hospitals will be built at Birmingham's NEC and the Manchester conference centre and will be ready later this month.
It comes as the UK once again saw its biggest daily increase in deaths - 563 - taking the overall toll to 2,352.
The government is facing growing pressure to increase the testing of medics, so that those who are self-isolating unnecessarily can return to work.
In a video message posted on Twitter, the prime minister, who is self-isolating after contracting the virus, reiterated the government's commitment to "ramp up" testing.
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