I first found the 1901 entry of John William Callow through "Royal Navy" on Ancestry.uk However on checking the first page of the actual census form it said "Prince of Wales PS" and over 30 of the crew had Manx Names or a few English names closely associated with the Isle of Man. So it seems he was a fireman on one of the IOM steam packet boats. A good clue.

Not that it really matters anymore but the battleship "Prince of 'Wales" was launched 25 March 1902 according to Wikipedia.