|Plymouth Naval Memorial|
The Commonwealth War Graves site has a single database for all services and nationalities, and for both world wars. The records recently added to Ancestry.com are for the First world War only, and comprise two separate databases. First there is the 'British Commonwealth War Graves Register 1914-1918' which contains entries from only about 250 cemeteries in three countries; most of them are in France, with a few in Belgium and Iraq. The source is the series of books printed by the Imperial War Graves Commission (as it was called then) in the 1920s. I compared a number of entries in these books with their equivalents on the Commonwealth War Graves Commission (CWGC) site, and found no differences, except that in a few cases the printed books said 'killed in action', 'died of wounds' or 'died of disease', which did not appear on the website. I did find one entry where the CWGC gave the wrong date - 1916 instead of 1918 - but the correct date was in the book.
So there doesn't seem to be any great advantage in using Ancestry for these war deaths, beyond the outside chance of finding a entry that had been mis-transcribed by the CWGC. We can already check 'Soldiers Died in the Great War' for place of birth and place of enlistment, a database which is available on more than one site. But there is one advantage to using Ancestry; not for the information it gives, but for the search engine. If you put a place name in the Keyword(s) box you can find men from a particular town, and the name search finds names of next of kin as well as the fallen soldiers - try putting in female names and you will see what I mean.
The second set of records is 'UK, Royal Navy and Royal Marine War Graves Roll, 1914-1919' and for all the entries that I compared provides more detail than the CWGC. This often includes next of kin information, and exact birthdate where the CWGC just gives an age at death. I also found a number of cases where the CWGC gave only initials, but Ancestry's database provides full names. So this is definitely worth using, even if you have already found and entry for your sailor or marine on the CWGC site - with a couple of exceptions. First of all, the men listed are in the Royal Navy or the Royal Marines, but not the Merchant Navy, although I found a member of my own family there who was a merchant seaman, but whose ship had been commandeered by the Royal Navy, so there should be others like him. Ancestry's description of the records suggests that the database contains records of Royal Navy and Royal Marines officers, but I could only find records of other ranks. One section of the description refers to the War Office, and seems to apply to the Army rather than the Royal Navy and Royal Marines, whose records were kept by the Admiralty. I will need to investigate further to get to the bottom of this. Watch this space.