Some 200 armed forces personnel are being made available to hospitals across the capital, which has been the epicentre of the Omicron outbreak with a huge upsurge in cases.
The MoD said the deployment includes 40 military medics and 160 general duty personnel to help fill gaps caused by absences due to NHS staff unable to work because they are ill or having to self-isolate.
They will be deployed in 40 teams of five – comprising one medic and four support personnel – and will be targeted at areas where the need is greatest.
It is expected they will be “on task” for the next three weeks.
In addition, 32 military co-responders are being provided to support the South Central Ambulance Service, working alongside paramedics until the end of March.
Defence Secretary Ben Wallace said: “The men and women of our armed forces are once again stepping up to support their dedicated colleagues in the NHS as they work hand-in-hand to protect the nation from Covid-19.
“They have shown their worth time and again throughout this pandemic, whether driving ambulances, administering vaccines or supporting patients in hospital, and they should be proud of their contribution to this truly national effort.”
However, the Royal College of Nursing’s director for England, Patricia Marquis, said the deployment meant the Government could no longer deny there was a “staffing crisis” in the NHS.
“The Prime Minister and others can no longer be dismissive of questions about the ability of NHS staff to deliver safe care,” she said.
“Once the military has been brought in, where does the Government turn next in a bid to ‘ride out’ the wave rather than deal with it?”
Around 1,800 service personnel are already deployed across the UK to support the civil authorities in their response to the pandemic.
They include 313 personnel who have been made available to the Welsh Ambulance Service NHS Trust and 96 to the Scottish Ambulance Service.
More than 1,000 service personnel have been provided to support the vaccine booster programme.