Your bell is indeed a ship bell from England. It was made during the reign of George the VI, hence the GR IV for George Regent the IV.
I have this exact bell and also one marked ER that is older and slightly different.
I believe these bells were most likely used on all military ships and possibly other significant vessels. The right to use the stamp of the monarchy is bestowed only to a few quality tradesmen by each King or Queen.
hope this helped.