Operation Walnut was a four-month long investigation targeting an organised methamphetamine supply-and-distribution ring operating out of the Mongrel Mob Porirua in the Wellington region. The investigation began in December 2016 when New Zealand Police officers infiltrated the Mongrel Mob via placing undercover officers as associates of the organisation, where they would buy methamphetamine from the gang. As well as undertaking 8 search warrants in the Wellington region, the Operation also targeted a property in the East Auckland suburb of Howick where the Mongrel Mob is suspected of importing the methamphetamine. The operation involved another 150 New Zealand Police officers, with 120 operating in the Wellington raids and the remaining 30 operating in the Auckland raids. From December 2016 to April 2017, it is thought that the Mongrel Mob had distributed over 20 kilograms of methamphetamine, valued at over $18 million.