To add to the information already given, some of the men are wearing the grade designator on their sleeve of 'Seaman Torpedoman second class', in the form of the torpedo shape with a star above it.
The particular medals are the three standard medals given to all servicemen who served in the appropriate time. The star shaped badge is either the 1914 Star (service before 23 November 1914) effectively for men already in service when war broke out or the 1914-15 Star (service before 31 December 1915) effectively for men who volunteered rather than waited for conscription in 1916.
The other two round medals are the British and Victory medals.
Some men may only have the last two mentioned medals, meaning they served from 1916 onwards, whilst some have none, meaning they did not serve 'in theatre' during the war at all. Or they just did not wear the medals that day !