This is despite the Armed Forces' response to COVID-19 becoming the biggest ever homeland military operation in peacetime, with more than 5,000 personnel involved.
The charity is now calling on the public to find out more about the work of the Armed Forces and celebrate their contribution in the fight against COVID-19 this Armed Forces Day – on Saturday.
The survey of 2,004 members of the British public aged over 16 was carried out in May.
They were asked: 'Who, of the following, do you admire the most due to the work they have been doing during the pandemic?'
Of those surveyed, 40% said they were unaware the Armed Forces have supported the fight against COVID-19, with 53% surveyed not knowing the Armed Forces helped with the UK's vaccinations.
Military personnel's help during the pandemic includes the vaccination roll-out, community testing, setting up Nightingale facilities, including hospitals at London's ExCel and Birmingham's NEC, laboratory work and PPE distribution and delivery.
More than half (54%) of those surveyed were also unaware of Armed Forces Day – a national day in the UK to celebrate the work of servicemen and women.
And 75% of those surveyed admitted they have shown no appreciation – saying thank you or donating to charity – to members of the Armed Forces for their work in the COVID effort over the last 18 months.
Sir Andrew Gregory, CEO at Armed Forces charity SSAFA, said: "The Armed Forces have worked tirelessly to support the country in the fight against the COVID-19 pandemic, including supporting the NHS and the Government with the nationwide vaccination roll-out, testing and much more.
"Hence the findings from our survey, highlighting the lack of understanding of the contribution of the Armed Forces, are a surprise to us at SSAFA.
"Therefore, it is appropriate that, for Armed Forces Day 2021, SSAFA and other organisations highlight the outstanding work of those in the Royal Navy, Royal Marines, British Army and Royal Air Force, alongside other key workers, who have all put themselves on the frontline in the fight against COVID-19.
"That is the essence of service, something that makes our Armed Forces so special," he added.
Sally Orange, an award-winning veteran and SSAFA fundraiser, volunteered at London's NHS Nightingale hospital and helped to support the NHS.
She said: "The last 18 months have been incredibly difficult for everyone, but particularly for our key workers.
"This includes our serving personnel who, in a time of crisis, stepped up and supported on the frontline in the fight against COVID-19.
"It is important that we take the time to pause and give thanks to them this Armed Forces Day.
"As a former Army physiotherapist, I volunteered to be a part of the effort working at the NHS Nightingale Hospital at ExCel London," she added.
"The military ethos was what led me to volunteer to help and I worked alongside many others from our Armed Forces – each of whom dedicated their time to bettering the lives of others when most in need."
She added that lockdown has "brought the very best out in people".
"It's been a real pleasure and honour to play even just a small role in what has been a collective, national effort," said Ms Orange.
In 2020, SSAFA supported more than 79,000 people in need, including veterans and their families.
The charity said it saw a significant change in the requests for support, with a greater focus on debt, housing, and relationship breakdown. Many of these issues were linked to mental wellbeing, loneliness and isolation.
Cover image: MOD.