[1] Langdon was born in Adelaide, served in the Royal Australian Navy during the Second World War, skipped university in favor of a writing career, and spent six years exploring South America.
[2] One of the first major projects he supervised as the executive officer of the PMB in the 1970s was the microfilming of more than 2,100 logbooks of American whaling, trading and naval ships active in the Pacific in the 19th century.
[3] Langdon's research on the history of Amanu island and the possible origin of antique Spanish ship cannons discovered on the atoll in 1929 resulted in his book The Lost Caravel.
[4] In this book Langdon presented evidence for his theory that the cannons were from the San Lesmes, a ship of the Spanish Loaísa expedition.
New Zealand film maker Winston Cowie's books Conquistador Puzzle Trail (2015) and Nueva Zelanda, un puzzle histórico: tras la pista de los conquistadores españoles (2016), published with the support of the Embassy of Spain to New Zealand, address the San Lesmes theory and consistent with Langdon's theory propose that it may have been wrecked in New Zealand, with oral tradition from elders on the Pouto Peninsula recording a wreck described as 'Spanish', and helmets and armour that had been found in the sand and caves of the peninsula.