In September 1984, Ferris attempted to import seven tons of explosives, firearms and ammunition, as well as medications, training manuals, and communications equipment, using the fishing vessel "Marita Ann", which was piloted by Mike Browne, another IRA member. The plan involved rendezvousing with the trawler "Valhalla", captained by Bob Anderson, which sailed from Boston, Massachusetts, transferring arms and ammunition to the "Marita Ann" and sailing to the south coast of County Kerry, where a number of cars were on standby to deliver the weapons to various Provisional IRA arms dumps. The "Marita Ann" was intercepted by the Irish Navy vessels the LÉ "Emer" and the LÉ "Aisling" off the south coast of Kerry with the weapons and ammunition on board. The crew were arrested. On 11 December 1984, Ferris and two other members of the "Marita Ann" crew, including Browne and a United States citizen, John Crawley, were sentenced to ten years imprisonment at Portlaoise Prison. Gavin Mortimer and John McCarthy both received suspended sentences. He was released on 11 September 1994.