As many as 5,200 military personnel were absent from duties because they were self-isolating under coronavirus rules, while a quarter of staff are yet to receive a vaccine, official figures show.
The revelation led to increased calls on Friday for the Government to take “urgent action” by changing quarantine rules as restrictions are relaxed in England and infections rise.
Ministers are planning to exempt the fully-vaccinated from quarantining over close contacts but will not introduce the change until August 16, around a month after most restrictions end.
The delay has led to warnings of a “pingdemic” leading to swathes of staff forced into isolation, with 530,126 alerts having been sent in England and Wales during the first week of July.
Ministry of Defence figures show 5,200 regular and reservist armed forces personnel were reported absent from work due to self-isolation over infection or as close contacts on July 1.
That is nearly 3% of the 198,000 personnel available to the Army, Navy and Air Force.
The figures also showed that there was no record of around a quarter of personnel – 54,742 – having received a coronavirus vaccine as of July 5.
Tobias Ellwood, the Conservative MP who chairs the Commons Defence Committee, warned that national security could be endangered if the figure continues to rise to 10%.
“When the scale of mass isolation caused by Covid-19 app starts hitting the operational effectiveness of our armed forces it’s time to urgently review the protocols,” he told the PA news agency.
“Even with rising infections it’s clear the app’s sensitivity could trigger a national security risk if a disproportionate scale of manpower is forced to isolate.”
Layla Moran, the Lib Dem MP who chairs the all-party parliamentary group on coronavirus, urged the Government to take “urgent action” to prevent a further hike in isolation numbers.
“The Government’s failure to keep Covid cases under control is now threatening the readiness of our armed forces,” she said.
“Ministers must explain what they are doing to address the risks posed by their road map to our national security.”
Labour’s shadow defence minister Stephen Morgan added: “These concerning figures demonstrate that ministers are falling short of their solemn duty to protect our serving personnel, who continue to perform vital work at home and abroad.
“The Government must immediately set out a clear and credible plan to step up vaccinations for our service personnel, and particularly those who are on deployment.”
The figures were released by defence minister Baroness Goldie as a written answer to a question from Crossbench peer Baroness Masham.
This week it emerged that the Carrier Strike Group including the Royal Navy flagship HMS Queen Elizabeth has been struck by a Covid-19 outbreak.
Last month, Defence Secretary Ben Wallace and and the heads of the Royal Navy, RAF and Strategic Command were told to isolate at home for 10 days.
They were alerted by the NHS Test and Trace app after coming into close contact with Chief of Defence General Sir Nick Carter, who tested positive during routine Covid-19 checks.