Two couples who posted assault rifle parts disguised as fishing kit home from a US holiday have been sentenced.
Carlos Sen, 26, has been jailed for three years and his half-brother Stephen Gibson, 46, was sentenced to two years at Nottingham Crown Court.
Rebekah Simons, 25, and Louise Caswell, 39, were handed suspended sentences.
The National Crime Agency (NCA) said Sen and Simons recruited a US resident in Florida to purchase the gun for them from a legitimate firearms collector.
The agency said it began investigating in June 2017 after US Homeland Security agents intercepted the parcel posted from Florida.
It was about to be shipped to Retford, Nottinghamshire, and contained the AR15 assault rifle's lower receiver, barrel shroud, magazines and stock.
The NCA said officers, working with Border Force, intercepted a second package in the UK which contained the rifle's barrel.
Days after the importation, couple Caswell and Gibson, of West Hill Road, Retford, were arrested by NCA officers.
Sen, of London Road, Retford, subsequently fled to Italy and was arrested, along with partner Simons, of the same address, after returning to the UK.
Adam Warnock, from the NCA, said: "This group made a foolish and blatant attempt to import a potentially lethal weapon into the country.
"Although gun crime in the UK remains relatively low compared to the US or mainland Europe, we know illegal firearms are used in acts of serious violence and by crime groups to coerce and intimidate."
The four defendants were all found guilty by a jury on Wednesday of conspiring to possess a firearm and conspiring to fraudulently evade any duty, prohibition, restriction or provision.
Simons was given a 21-month sentence, suspended for 21 months, and Caswell was handed a 15-month sentence, suspended for 21 months.