You might like to see the attached website explaining how navy numbers evolved. The correct term by 1912 is 'Official number', but I doubt that is really material here.
As with anything associated with genealogy, it is not as simple as you might hope.
Ancestry has both navy and army records in it.
The site below says the navy used 6 digit numbers from 1894, adding a letter prefix in 1908. So, presumably your number should be a letter followed by 6 numbers.
The army tended to use 4 or 5 digit regimental numbers which could be repeated many times across different regiments. In 1917 the Territorials introduced a 6 digit number, without the letter prefix used by the navy.
So, it depends if you have the prefix letter or not. If you do not have a prefix letter, there could be the same number used in the Territorials.
However, the record that comes up SHOULD clearly show if the person shown is navy or army. Once the record is looked at, it should not be in doubt. I am not sure if navy records were included in the losses caused by the blitz.
I suggest trying the search in variable ways, ie, adding or subtracting the various prefixes.
You might be able to determine his role by reference to the website.http://www.godfreydykes.info/ROYAL%20NAVY%20OFFICIAL%20NUMBE...