Rank of Writer 3rd Class (1914-18)

Am in the USA next couple of weeks and while in Washington DC I intend going to Arlington National Cemetery, where there are some 26 British graves that come under the auspices of the Commonwealth War Graves Commission [CWGC]. They are a mixture of 1914-18 and 1939-45 and come from all services including Royal Navy, Royal Marine and Merchant Marine.
The official website for the cemetery has some errors [http://www.arlingtoncemetery.mil/Explore/Notable-Graves/Minorities/Foreign-Nationals] e.g the merchant seamen are given as 'Royal Navy', an army corporal of Royal Signals given the rank of 'captain'. The main one that made me smile was a 'writer 3rd class' , given the title of 'Mr'! Evidently the US military hadn't come across the writer branch in the RN
The deceased is shown on the CWGC web site as SYMONS , THOMAS HENRY, date of death 21/12/1918, rank Writer 3rd [Class], Royal Navy , H.M. Yacht "Warrior." ; Service no. 'M/18229'.
I'm contacting the American authorities to point out their website errors etc.
Just so I'm fully armed, what rank would a writer, 3rd class be? Ordinary seaman or what? As no age is given could he be a Boy'? Secondly, re his service number, what does the 'M/' stand for. Pardon my ignorance but I'm a military historian dipping my toes into the arcane world of matelotery [However, when I was a child I went onboard an 'O' class submarine visiting South Wales, does that count?).

Deleted 59428

A Writer 3rd class would be the equivalent of an Ordinary Seamen, he would be bottom of the heap, straight out of training.

This site lists WW1 era branches if that helps


The M in WW1 denotes his branch as explained on this site

http://www.godfreydykes.info/ROYAL NAVY OFFICIAL NUMBERS [RATINGS].htm

And no, visiting an O boat doesn't count ;)

http://www.gwpda.org/naval/rn_ranks_and_rates_table_1918.pdf explains all


War Hero
Super Moderator
To all who have helped....many thanks. I looked at the page re letter prefixes for Navy numbers and I had to go for a lie down!
That page isn't completely up to date, when I joined up all numbers issued started with D, P for Marines, C for officers and W for females, followed by 6 numbers and ending with a letter, just before I left, letters were dropped and it's now just numbers as it's easier for computers.