In February 2005, Celtic Link Ferries began sailing between Rosslare and Cherbourg. The European Diplomat was brought from P&O who had previously operated her on the route, but were forced to close the route as a result of economic difficulties at Cherbourg.

A French freight operator was said to be interested in operating the service but as the European Diplomat's last sailing looming, and farmers' organisations criticising the closure, the six O'Flaherty brothers, from Wexford unexpectedly stepped in by purchasing the European Diplomat and manning services from P&O for  10 million.

The former P&O vessel then had her name shortened to Diplomat, and resumed her sailings to France.

In March, a short lived weekly rotation to Pembroke began, with outward bound sailings departing Rosslare on Mondays at 16.00 and the return sailing arriving at Rosslare at 05.00 the following day.

In May 2006 Celtic Link launched a Dublin - Liverpool route with the Celtic Star (ex Northern Star). She was joined in January 2007 by the Celtic Sun (ex-Carmen B). The two ship route was handed over to Seatrucks in September 2007.

In March 2007, Celtic Link announced plans to launch a new Cherbourg to Portsmouth service with the Celtic Mist. However on arrival in Portsmouth, she was not deemed fit for passenger services an inspection by the UK’s MCA, and was moved to Southampton for further work, but Celtic Link decided not to take her up on charter, and was returned to her owners.

In 4 October 2009 Celtic Link Ferries again tried to start English Channel services, announcing they have chartered the Norman Voyager from LD Lines to join the Diplomat sailing Portsmouth – Cherbourg - Rosslare. On 19 November 2009 the Norman Voyager was detained in Portsmouth by the Maritime and Coastguard Agency when the crew failed a basic test of emergency procedures. In December Celtic Link then announced that they were indefinitely suspending the service, and instead used her to increase capacity on their Rosslare – Cherbourg operations.

Meanwhile, the Diplomat was laid up pending charter, first in Dublin then Waterford. In April 2010 she was leased to Marine Express and sailed to Puerto Rico.