Why Australian Oberons received Mark 48 torpedoes

Why were the Royal Australian Navy's Oberon-class submarines fitted for Mark 48 torpedoes instead of British weapons?

The arrangement combined a British-built submarine with American weapons supply and logistics, strengthening interoperability with both partners.

Australia could retain the proven British Oberon design while drawing ammunition from American supply lines. The Mark 48 fit supported operational ties with the United States and simplified access to its logistics network. It also let the Royal Australian Navy straddle two important defence relationships. The result was a British submarine paired with an American torpedo system for practical alliance reasons.