Human traffickers crammed 29 Vietnamese nationals, including 17 children, into Britain on a yacht.
The four men then bundled the group into the back of a van, which had been parked in the harbour car park.
The victims were then "carted around like freight" as the defendants "traded in human misery".
But Jon Ransom, 63, Glen Bennett, 55, Frank Walling, 72, and Keith Plummer, 63, have now been jailed for more than 15 years in total.
Speaking after the case at Truro Crown Court, Detective Inspector Glenn Willcocks, of Devon and Cornwall Police, said: "The vessel was in a poor state, smelling strongly of diesel and cluttered with clothing and empty food wrappings.
"The boat would have been extremely cramped with all 29 people having to share a single toilet.
"The four convicted today risked the lives of 29 men, women and children without any appreciation of the danger of their circumstances.
"They were motivated only by monetary reward and thankfully no one paid the ultimate price."
Several members of the public saw the group of people getting off a boat at Newlyn Harbour, Cornwall, on April 12 last year.
CCTV footage reviewed the van, followed by another car, and police stopped both vehicles on the M5 near Cullompton, Devon.
The van door was opened and officers found 29 Vietnamese nationals inside, including women and children.
They were taken to a multi-agency reception centre and referred to the Home Office and social care services to be managed, Devon and Cornwall Police said.
The men were arrested but initially denied any wrongdoing.
However, Judge Robert Linford, sentencing the men, said they were motivated by profit and "traded in human misery" with the victims "carted around like freight".
It is believed that the 29 victims boarded the yacht, which was called the Johan Sebastian and owned by Walling, in Roscoff, France.
Walling, from Colne, Lancashire, and Bennett, of Burnley, Lancashire, crewed the yacht.
Both they and Ransom, of Kent, were sentenced to four and a half years in prison. Plummer, who is from Sheerness, Kent, will serve three years and four months.
They were convicted under section 25 of the Immigration Act - assisting unlawful immigration.
Ann Hampshire, senior crown prosecutor for the Crown Prosecution Service, described the trip as "carefully planned".
She said it was a "well organised operation involving people and places in different parts of the UK, carefully co-ordinated to facilitate illegal entry into the UK".
