Around 750 Armed Forces personnel have been made available to help the acceleration of the UK's COVID booster vaccination programme.
The hundreds of servicemen and women will help deliver jabs and co-ordinate the rollout in England and Scotland.
Currently, there are more than 100 personnel supporting the booster vaccine rollout in Scotland, with 600 Armed Forces personnel now being made available to NHS England to administer the top-up vaccines in small teams across the UK, as well as 50 involved in planning.
Chief of the Defence Staff Admiral Sir Tony Radakin said he is "proud of our Armed Forces who are once again stepping up to help protect people and communities".
"We have a long history of working hand in hand with the NHS as two organisations with a common goal – to help keep our people safe," he said.
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Roughly 50 personnel will also provide planning support to NHS England.
More than 40 planners will be deployed to NHS regions across England and 10 logistics experts will be based at NHS England's headquarters in London.
Defence Secretary Ben Wallace said the personnel have been "rapidly mobilised" to work alongside healthcare professionals.
"Our Armed Forces will help to get vaccines into arms as quickly as possible as we continue our efforts to support the UK's response to the pandemic," he said.
Planners based at NHS England headquarters will be led by Brigadier Phil Prosser – previously deployed to support the delivery of the initial vaccine programme which began in December 2020.
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They will work alongside NHS England to maximise existing capacity and ensure the booster programme can be delivered quickly.
Health and Social Care Secretary Sajid Javid said the UK is "turbocharging our COVID-19 booster programme to offer every adult in England a vaccine by the end of the year".
"Building our defences through boosters is a hugely important national mission and it's brilliant to see the military supporting our NHS staff in our race against the virus," he said.
Since March 2020, defence has supported more than 430 tasks as part of Operation Rescript – the military's support to the UK's response to the pandemic.
Defence is currently supporting ambulance services in Wales and Scotland and the vaccine rollout in Scotland, with tasks including testing.