A number of personnel at HMS Raleigh in Cornwall have tested positive for coronavirus.
A passing out ceremony at the site, which is used to train new Royal Navy recruits, has been cancelled due to the COVID-19 cases.
The parade had been due to take place on Friday.
A Royal Navy spokesperson said: "We can confirm that a small number of personnel at HMS Raleigh tested positive for COVID-19 and are under medical supervision.
"Personnel identified as having been in contact with those who have tested positive are self-isolating in line with Public Health England guidance.
"Due to the COVID-19 cases and the personnel who have to self-isolate, we have now taken the precaution of cancelling the passing out parade due to take place on Friday 18 September."
HMS Raleigh is the Royal Navy's largest training centre in the south-west of England, featuring a 239-acre main site and a maritime training centre on the River Lynher.
Ratings from all branches of the service receive their 10-week basic training there, with around 2,200 people on site on an average day, according to the Navy.
The Royal Navy continued to carry out basic training at HMS Raleigh during the coronavirus pandemic by following a number of measures.
The Navy said the base, which trains new recruits, had been able to deliver essential training in line with advice from Public Health England.