The cap ribbons have been confirmed as being HMS GANGES. You maybe interested in the following info most of which has come from an oppo.
At first glance (and a quick one at that) the three badger is PO 1st Class. As he has no crown above his trade badge this would be (a) Qualified Signalman, higher standard, class 1 1904-1909 (b) Yeoman of Signals 1909-1932. That is just a change of name the badge was the same. POs did not receive fore & aft rig until the 1920s (I think 1923). Sparkers badge was not introduced until 1909. So, I think the photo is possibly pre 1909. You will note the black silk is a bit roughly tied, this because it was square and not stitched. The rectangle one stitched didn't come in until 1934.
The 2 (presumably) Instructors are wearing white caps (But see further down) which to me seems odd given the apparently early date but alternatively fits in with badge Boys, leading Boys (of which I was one) wearing white gaiters. I will ask my contact. The photo was found in Brighton in a tin of photos by a Bootneck who passed it on to a member of the Comms branch. I have added A to the caption of the first photo and B to this photo for clarity. More to follow in due course.
The training of comms boys did not start at Ganges until 1909 when Lt Eyre’s arrived there to start the signal school originally concentrating on semaphore and flag signals. He was responsible for creating the sigs division – this was fully operational by 1913 with both visual and wireless telegraphy.
The back of the attached photo (B) has the title Early VS Class at Ganges - the original photo is now in the museum - it looks as though this class has the same instructors, maybe the hats will give a better idea of the date. Regarding photo A - From the original poster elsewhere: He (The Bootneck) told me amongst the other items (in the tin) was some Jewish books so thinks the lad was Jewish no other details. I will have to search for white cap covers so will send later. I think offhand that at this time they were just white cap covers and not white caps.
Also offhand, if the instructors are the same in both photos the 'sennet hats' were abolished in 1920s (I think 1921). It seems that the first time a white (duck) cap for ratings appears in dress regs is 1906 (Navy List). This was in addition to the sennet hat and 2 blue cloth caps.1914.
Round about 1910-1914 white caps or white cap covers (ratings were issued with both) and white fronts were worn: At home – with blue uniform jumpers and trousers from 1st may to 30 September. Abroad – or sennet hats when ordered. With white clothing at discretion of the senior naval officer present. Given that the photo was taken between 1909 and 1914, the two instructors would have been Petty Officers, the unified rate of which was introduced in 1907 and the PO’s badge (previously worn by 1st class POs), which still exists today, was introduced.
1879 regs: White cap covers only for use in warm climates when white dress is worn (I am presuming that includes UK summer time).
1890 regs: White cap covers always to be worn with white working dress (sennet hat with best dress) maybe worn with blue clothing if necessary as protection against sun.
1897 regs: ditto
1914 regs: Boys on being kitted up for sea, cap white duck 1. Which relates to the comment ref boys blue caps. The frustrating bit is, somewhere I'm sure I've got the date of when white caps were first issued.
Ref the last comment: White fronts and sennet hats classed as No1 best summer dress. Winter rig, navy blue pullovers would have been worn. It seems that the first time a white (duck) cap for ratings appears in dress regs is 1906 (Navy List). This was in addition to the sennet hat and 2 blue cloth caps. (Apols for being long winded for obvious reasons - in summary the photos were taken pre WW1 and the 2 Instrs. were P.O.s)