Wunper, I think Rallye has the description spot on if we are thinking of the same maneouvre which I know as a Roll Under break.
In a Derry Turn the aircraft is in a turn before starting the maneouvre but this one is started with the wings level.
I have seen it used by an aerobatic team as a different way to enter the circuit, with the aircraft in opposite echelon to the normal.
IE. if intending to break to the left the aircraft are in echelon port and the turn is into 270 degree barrel roll to ensure that each aircraft is turning under those following.
However, this has its dangers because the aircraft lose sight of each other once the turn is commenced and for that reason I think it is no longer used.