Yeoman of Signals
A supervisory trade in the Royal Corps of Signals, formed from Operators. In the good old days, this meant that a Yo-person had to be Class I in one operator trade and at least Class II in another, before embarking on selection and training for the exalted role of 'Yeoman'. Rank ranged from SSgt to WO1 and LE commissions 'in trade' were/are referred to as 'Traffic Officers'.
A YoS could bore the pants off any operator under him given the opportunity and a captive listener. A YoS, however, generally looks after the Unit Ops Office as the FoS swans off on another technical course that has no relevance to the job he is currently doing! Yeoman is always better looking that the Foreman.
Master of Communications: highly-skilled in operating and managing the Corps radio communications. Derived from what used to be called God's Trade. The Mighty Yozza can be found dishing out CEIs as opposed to extras. He loves assigning freaky frequencies which are shared with Ishmal's Taxis in Turkey.
Apparently in the TA there were two TA-specific roles for YoS - namely Yeoman Of Signals (National Communications) and Yeoman Of Signals (Ptarmigan), though the author is not certain if these roles survive.
A TA YoS does the eighteen-month course in two weeks. These are the bane of all regular YoSs' lives as they did the course and seem to have forgotten all of it - and in such a short time. He is the key man in most TA signal units, apart from the barman and is supposed to have his finger on the pulse, but the corpse is probably dead.
Normally a RS, or Radio Operator Class I and crypto-trained (supposedly) and thus ready for the ultimate challenge. Either comes from an NCRS, Ptarmigan or CNR background. Some like to think they are indespensible, whilst others gain a lot of experience and pass it down to the troops. A few have visited the Sandpit or BLMF and never want to see a piece of paper with holes in it again.
More YOS here.