Green post boxes

I've been a fan of these postboxes for a while now.
If you see beyond the green - Irish National Colour, don't forget! - and look at the writing on the box above, you'll see a crown sitting above the letters ER.
There are also postboxes with VR and others with GR.
The British Monarchs they refer to are:
George V 1910–1936 (26 years reign)
Edward VII 1901–1910 (9 years reign)
Victoria 1837–1901 (64 years reign)
I've never spotted one with WR but if it existed it would be even older and would refer to:
William IV 1830–1837

The story goes that when the Irish republic was formed, we couldn't afford new postboxes and the good cast iron ones that were in place were perfectly functional - so we simply sent people around with buckets of green paints and thereby nationalised our postboxes!