Serving members of Britain's armed forces, many of them under 18, have been referred to the anti-terrorism Prevent programme.
Most of the cases involving personnel from the Army, Royal Air Force and Royal Navy were linked to far-right extremism, figures obtained by The Guardian newspaper showed.
Fourteen investigations of serving personnel were carried out in 2019, while an undisclosed but smaller number took place this year and last.
Authorities warned of a rise in far-right online grooming during Covid-19 lockdowns, with young people the most vulnerable.
Police said last year that 10 of the dozen under-18s in the military arrested in 2019 for terrorist sympathies were linked to right-wing ideologies.
Senior military officials, meanwhile, are tracking the rise in far-right activity, which is in part considered to be a reaction to the threat of Islamist extremism in the UK.
A 2017 document that was leaked online and detailed signs of far-right views within military ranks was given to senior British Army officers.
Signs included describing multicultural towns as “lost” and adding “-istan” to British place names.
In the same year, four soldiers were arrested, accused of links to National Action, a far-right group banned in 2016 after its members celebrated the murder of MP Jo Cox.
The four included Corp Mikko Vehvilainen, who served in Afghanistan and in 2018 was sentenced to eight years in jail for belonging to the group.
Vehvilainen was described as a recruiter for National Action within the Army.
At his trial, the married father of three was described as a self-confessed racist with repulsive views about black people, Muslims and Jews.
He planned to turn a village in Wales into a whites-only stronghold for a race war.
Police raids at his home uncovered Nazi paraphernalia and photographs of Vehvilainen making a Nazi salute.
Another suspect was acquitted of membership of National Action but his trial was told he had a cardboard swastika on open display at his barracks in Cyprus.
Britain set up the Prevent scheme in 2006 to stop people from being drawn into terrorism.
