Australia: 1917-1988.
Northern Territory Post Offices - slogan date stamps.
Only one Telegraph slogan - fittingly for the OVERLAND TELEGRAPH LINE CENTENARY - was used in the Northern Territory. It was used at two Offices - Alice Springs and Darwin - in August 1972:

Both date stamps were circular. Both are rare to find.

Alice Springs.

Overland Telegraph Line Centenary.

Datestamp: Circle (diameter: 21 mm).

Base inscription: N.T. AUST.

Characteristics:
 Die 5A: A spans GR.

Only recorded date of this format:
21 August 1972.

Number in the Census: 1.

 Overland AS21 August 1972.

Darwin.

OVERLAND TELEGRAPH LINE CENTENARY.

Datestamp: Circle
(diameter: 21 mm).

Base inscription: N.T. 5790

Only recorded date of this format:
8 August 1972.

Number in the Census: 1.

 Darwin
8 August 1972.