Andrew Donald Steele, 66, of Yankalilla, on the Fleurieu Peninsula, was sentenced in the SA District Court on Friday after pleading guilty to seven charges.
He was arrested in May 2023 after Border Force officers found an image of a child on his phone when he returned from Indonesia.
A subsequent investigation established that he had travelled to the Philippines in April 2018 to meet a woman named T. Over the next month, he abused her daughter CR, aged 9, and her sister, CH, aged 5, witnessed the abuse.
Judge Paul Muscat said Steele had corrupted the girls' mother, exploiting her poverty and vulnerability, and the abuse continued via video calls after his return to Australia.
After his arrest, police found 12,470 images of child abuse material and 126 videos of child abuse material on his electronic devices.
A review of his internet history revealed that between April 2022 and May 2023, he visited child abuse websites on an "incredible" 3679 occasions.
He also met a woman through a dating site, Filipino Cupid, and exchanged child exploitation material with her.
"Given the nature of the conversations between the two of you on Facebook Messenger, it is clear that there exists a dark market in the Philippines where people like her engage with deviant and depraved men such as yourself, who are sexually interested in the abuse of young children," Judge Muscat told Steele.
Judge Muscat said Steele's communications were "revolting as much as they are depraved".
"Indeed so graphic and depraved is the content of your conversations that I am not prepared to repeat them in these remarks, other than to indicate that they involve extremely young girls being raped in various ways and taking pleasure from that," he said.
Steele, formerly of the Northern Territory, had retired to SA in 2019 with his family.
He had claimed that following the birth of his youngest son, sexual intimacy in his marriage "essentially ended" and he began trawling the internet, exploring and using pornography.
"Disturbingly, you also developed an appetite for child abuse material," Judge Muscat said.
"Your conduct is reprehensible and must be strongly denounced."
Steele's wife and eldest son wrote letters of support.
"While I totally understand that your family is struggling to comprehend how the husband and father they believe they knew could also have this darker and perverse side to him, I cannot accept their categorisation of you as a man of good character when you have, in fact, been committing some very serious child sex offences from at least 2016," Judge Muscat said.
The charges included persistently sexually abusing a child outside Australia, engaging in sexual activities with a child outside Australia, using a carriage service to disseminate child exploitation material, and possessing and distributing child exploitation material.
Steele's 15-year jail term included a discount for pleading guilty and co-operating with police. He will be eligible for parole after nine years, backdated to the time of his arrest.
1800 RESPECT (1800 737 732)
National Sexual Abuse and Redress Support Service 1800 211 028
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