To echo Infosending1’s comments about attaching a copy of the document to your message, even after looking many RN certificates of Service from a range of periods (columns and headers changed several times), except for some obvious abbreviations that appear in the documents it can still be very difficult to comment on a query such as yours without sight of the original document.
The certificates of service were created by the RN pay office, from the quarterly ships books to record a man’s service for pension purposes and were never intended for public consumption, so apart from the untidy writing and degradation of some characters during microfilming and subsequent copying, sometimes there are notes about qualifications or courses that link on the record with obscure symbols that can add more meat on the barebones of the list of ships, ratings etc. Timeline, dates, ships/shore stations and other information can also help unravel an apparently unknown abbreviation and of course letters are sometimes misread.
It’s like you saying, “initials QDD, OOD and 2DD against some postings”, I have to assume that the initials appear in the rating column but have no idea what went before any such initial appeared or what the “postings” refer too e.g. did it change while attending a course at a depot ship or shore establishment?
Again Infosending has picked up on your statement, “retire in 1922 as CPO and subsequently Lieutenant”, if he “retired” he must have rejoined, or did he transfer to the RFR (Royal Fleet Reserve) on being discharged with 20+ years service and was then “re-activated” for WWI.
I would also question your statement, “On his PO record are the initials QDD, OOD and 2DD against some postings” as his rating as Petty Officer would be on the same “record” (certificate of service) as the very first entry as an Ordinary Seaman.
Rating’s can be substantive (based on rank) e.g. B2C (boy seaman 2nd class, OS (Ordinary Seaman or Ordinary Rating, LS (Leading Seaman or Rating) or they can be non-substantive (a seaman’s trade or occupation) e.g. TM (Trained Man) one who had undergone basic instruction in a trade.
In reality the RN pay office didn’t always follow the headings on the certificates of service forms e.g a Stoker 2nd Class was an Ordinary Seaman rate and Stoker 1st Class was a Able rating, but they are found on certificates of service in the substantive rating column as that was the pay scale header; only the Leading rating is given and then it will be seen as Ldg Sto (Leading Stoker) in the substantive rate column and for almost every rate and trade there will be more than one way of writing it, so it is difficult to create a simple list of abbreviations to fit any certificate.
Some non-substantive ratings had to be re-examined at various periods and could lapse, pay was increased for a number of years at a particular rating and notes will sometimes be found indicating such. You may have already have noticed, that except for ships and associated periods of service etc., timelines are separately vertical within columns and not linked across the page, so some non-substantive rating, badges, character/conduct assessments and remarks have to be carefully linked to the ship timelines.
The above are just a few examples of why sight of the actual document is important. I know you can’t attach the NA’s pdf file to an Ancestry post so would have to print the certificate and then scan it (probably further degrading the quality) and attach it as a jpeg image.
Now to your abbreviations.
SG = Seaman Gunner and from 1871 torpedoes were being fitted in ships and all “junior” seamen gunners were given additional training in torpedo work and a new non-substantive rating was created as: SGT = Seaman Gunner Torpedoman.
Quite what the SGC relates to I cannot be sure; is the gap between the G & T greater than that between the S & G that possibly indicates a missing letter; a 1 perhaps indicating Seaman Gunner 1st Class? Certainly a gunner had to be qualified 1st class before receiving instruction in torpedoes, so timeline will be significant.
CG appears on every certificate of service, usually accompanied by a value in £ (GBP) and indicates a Clothing Gratuity was paid.
However, if CG appears in a rating or sub-rating column then again it’s down to context and timeline, but is likely to mean C (of) G = Captain of Gun, i.e. a rating in charge of a gun mount and he would be a leading seaman rate or above.
QDD = Qualified in Deep Diving, but OOD and 2 DD I’ve not come across in the ratings’ certificates I’ve seen; again context and timeline is likely to be important.
Although OOD can mean Officer of the Deck (or Day) and as a Petty Officer it could indicate he had qualified to carry out the duties of an OOD on a smaller vessel, for a rating I believe the OOD and 2 DD are probably related to diving qualifications, but again without sight of the document it’s impossible to say.
Re Good Conduct Badges & Pay
These will appear in the column with “badges” in the header (sometimes within sub-ratings column) and could be granted (G), deprived (D) or restored (R) are usually written with a date, a maximum of 3 badges that from 1860 to Jan 1919 were awarded for 3, 8 & 13 years service with conduct of VG or above and each badge attracted extra pay of 1d per day (old penny, 12p = 1 shilling (5 new pence); from Feb 1919 pay was increased to 3d per day per badge and from 1946 GCB’s were awarded for 4, 8 & 12 years with pay increased to 4d per day per badge.
Re his achieving the rank of Lieutenant, although rare, even today it is possible for senior rating (Petty Officer [PO] or Chief Petty Officer [CPO] to receive a Commission on merit and like for “other ranks” in the Army gaining commissioned rank during and after WWI, there are many similar examples of seamen receiving a commission in WWI, especially those in the RNVR who served ashore as infantry in France. In the RN a seaman who went through the progression of ratings from the lower deck (Seamen’s domain) to the Quarter Deck (officer territory) is referred to as “he came through the hawsepipe” and a “Hawse Pipe Officer”