Australia: Australian Post Office years: 1955-1975.
The Overland Telegraph Centenary delivery envelopes

In 1971, the printing company SGGS Graysmith was contracted to print all three types of envelopes to commemorate the Centenary of the completion of the Overland Telegraph Line. The September 1971 Post Office Monthly Circular contained the following announcement:

13. Telegram Envelopes - Slogan to Commemorate Overland Telegraph Line Centenary. - A centenary to commemorate the Overland Telegraph Line will be carried out in 1972 and it is proposed to include a slogan regarding this anniversary on the back of the telegram envelopes that will be used exclusively throughout the centenary year.

2. Postmasters are to ensure that sufficient stocks of these anniversary envelopes are on hand for use throughout 1972. As from 1st November 1971, all issues from the Supply Branch of TX 65 (ordinary rate) and TX 65H (confirmatory copy) envelopes will bear the special anniversary slogan. Postmasters receiving half-yearly supplies of stock prior to 1st November, 1971, should obtain these anniversary envelopes by requistioning in the normal manner please.

3. Use of these envelopes as early as December, 1971, is quite acceptable but should cease no later than early 1973. Postmasters and staff concerned should note accordingly, please. (N. 287/1/18).

All three types are the same in size, flap, size of window and schedule number.

Ordinary rate delivery envelope  
AA-EO-18Ca (71)
Used on 28 August 1972 at C.T.O. Melbourne.

AA-EO-18E (71).

Same format as the normal ordinary rate delivery envelopes.

Urgent rate delivery envelope  
AA-EU-9Ca (71) AA-EU-9Ca_rev (71)

AA-EU-11C (71).

Same format as the normal urgent rate delivery envelopes.

AA-EU-Ca_sch (71)
Confirmatory Copy envelope  

AA-EC-3C (71).

Same format as the normal Confirmatory Copy delivery envelopes.

AA-EC-3D_no sched
AA-EC-3Ca: no schedule number under the flap.
AA-EC-3Cb: schedule number under flap at right.

In August 1973, the Post Office Monthly Circular contained the following announcement to cancel the use of the envelopes:

14. Telegram Envelopes Bearing the Overland Telegraph Line Centenary Slogan. - Advice has been received that telegram envelopes TX. 65 (ordinary rate), TX. 65A (urgent rate) and TX. 65H (confirmatory copy) bearing the Overland Telegraph Line Centenary slogan should not be used after the 30th November 1973, and all surplus stock on hand after this date should be destroyed. (N. 226/9/165).