Australia
Danish Aeorgramme Form Used as Airmail Letter

Danish aerogramme form used in Australia (MELBOURNE 9 JAN 1968) as an airmail letter. The airmail letter rate per 1/2 oz to European destinations from February 14, 1966 to September 30, 1968 was 25c.

If it were posted as an aerogramme, the rate would have been 10c. But Australian postal authorities only allowed privately manufactured aerogramme forms to be used if the forms had been presented for approval before. 

The sender was a Danish crew member of M/S Nella Dan, a scientific research vessel, deployed for the A.N.A.R.E. (Australian National Antarctic Research Expeditions.

"Over the period Jan. 5, 1968 - Mar. 19, 1968 under the command of Donald Styles, on this voyage the crew carried out a topographical survey of the eastern side of the Amery Ice Shelf conducted from Nella Dan. A field station was established at the Amery Ice Shelf in Feb 1968 (occupied to Feb 1969)". [1]

He wrote his letter on December 25, 1967 on Macquarie Island, where A.N.A.R.E. had its headquarters since May 25, 1948 [2]. On January 5, 1968, M.S. Nella Dan was scheduled to leave for the South Pole ("Den 5 januar sejler vi till sydpolen").

Instead, the vessel first went back to Melbourne. According to the records kept by Australian Antarctic Division [3], M/S  Nella Dan

• Depart Melbourne:        Dec 12, 1967 
• Arrive Macquarie Island: Dec 16, 1967
• Depart Macquarie Island: Dec 26, 1967
• Arrive Melbourne:        Dec 31, 1967

From Melbourne M/S Nella Dan started to the Amery Ice Shelf. It is also mentioned in the records, that "the Deputy Voyage Leader collapsed and died at Macquarie Island on 24 Dec 1967". It is most likely that this was the reason for the extra trip to Melbourne.

References
[1] http://trove.nla.gov.au/work/31661761?q=subject%3A%22Nella+Dan+%28Ship%29+--+Maps.%22&c=map&versionId=38391593
[2] http://en.wikipedia.org/wiki/Macquarie_Island
[3] Information received from AAD