Linfox and ABV, page-22

Oh yes plough, one of those vehicles that could drive under water was the Austin Champ, it had an extention carburettor tube which when raised and locked in place allowed air into the carb, mind you below that level and you were in bother. It also had two gear sticks, one a normal 4 speed and the other was forward or reverse so that the gears could be changed in reverse, if you get the chance try it, it's weird looking back and changing gears.
I was conscripted in late 1958 so as you say it's not new technology.
The Austin Champ was the British answer to the Jeep only better.