I don’t think that’s quite accurate, Keiva – I can think of plenty of examples of cockney that work the other way about, such as “apples and pears” for ‘stairs’. Like most argots, the key is to draw a line between the insiders and the outsiders.

I am inclined to think you have hit the nail right on the head, sunny Gym – the original term would have been something quite pompous and officious like inflatable vest for which the substitution of “Mae West” would have been a natural inflation. To put it in context you have only to imagine the class-ridden system of England in that time: if the educated officers introduced new equipment with a fancy name, it would be imperative for the ranks to make it their own by a linguistic twist. But Rhuby is more expert on CRS than I – come on in, Rhuby, the water’s quite buoyant!