From info in Wikipedia, the British (i.e. Commonwealth) ship was named "Jervis Bay" after the place in Australia (a special territory of its own, but nestled within New South Wales), which is well known and popularly pronounced "Jarvis" although spelled "Jervis". According to WP, "Jervis Bay is named after Sir John Jervis, Admiral of the Fleet, Earl of St. Vincent, and first Viscount St. Vincent."
Apparently as far back as 1928, relatives of the "Jervis" family were complaining that the bloody natives were mispronouncing the family name, but hey that's just progress (?) :
According to other sources, the "Jarvis" pronunciation was also used in the navy for the ship in question.
However the matter is still a source of some disagreement:
"When controversy raged on the subject during 1972, the State Member for South Coast, Jack Beale (who was also Minister for Environment Control) sought to have it clarified by the Geographical Names Board of New South Wales.
While not giving a definitive answer, the GNB’s response in January 1973 was that once a place name had been established in this State, it’s pronunciation would be determined ‘by popular usage’ which said it was ‘Jarvis’.
However, during that month Shoalhaven Shire confirmed a previous resolution that the correct pronunciation was “Jervis”. "
- Tony Rees, Australia