When you're writing to somebody living in your own country, it's easy to send him a stamp
for the answer. The problem is more difficult when you're not living in the same country.
The solution since october 1907 is to buy at your post office a "reply coupon" which will be
exchanged in the other country's post office against a stamp covering the postal rate (surface
single letter, and now air mail letter) to answer you.
There are two main postal reply coupon families :
- international reply coupon (I.R.C) which follow rules edited by the Universal Postal Union
(UPU) and may be used almost in the whole world and
- reply coupons from restricted postal unions (France and its former colonies, United Kingdom
and Commonwealth, Arab postal union, and so on).
This is the VIENNA FORM VI 21 used from december 1965 to december 31st 1974. ("SeSi" coll.)
Heurté states that "The New Hebrides have received 5000 VI21 in the 2nd quater of 1974". These 2 IRCs extend this to an earlier date.