THEY approach the coast in the early morning, send landing parties numbered in hundreds to scour the locality, and slip away to sea again by evening.
But these are benign raiders, the cruise ships that are now bringing extra revenue and short-term visitors to a number of major Irish ports.
The first two cruise liners in a series of 18 this season, the Island Princess and the Berlin, have already called to Waterford carrying some 1,000 passengers - and more than 500 crew.
The programme of visits will continue until September, bringing a shopping boost to regional centres as far from the port as Kilkenny, and introducing a special category of wealthy visitors to Ireland's scenery and society.
Central to the safe handling of the sleek cruise vessels are the six professional maritime pilots who work at Waterford Port under the harbourmaster, Mr Philip Cowman.
This growing sector of the tourism market is co-ordinated locally by Waterford Cruise Co-Op, which includes the Harbour Commissioners, the Chamber of Commerce and Waterford Crystal. On a national scale, the marketing co-operative, Cruise Ireland, is promoting the business and has produced a comprehensive glossy brochure for the cruising visitors.
Cruise Ireland, formed in association with Bord Failte, links the principal ports, ships' agents, ground handlers, State agencies and chambers of commerce, with support from the Northern Ireland Tourist Board.
Ireland's ability to tap into the economic potential of the cruise business is opportunistic. With almost half of the world cruise business focusing on the Caribbean, and around 4 per cent on western Europe, the liners must generally be persuaded to call to Irish ports on the way to or from their main destinations.
This State may, for example, catch the cruises to or from the Norwegian fjords or on transatlantic voyages. Ireland can also be part of the dedicated west European tours, and there is an opportunity also with the smaller "soft adventure" cruises which are becoming popular. Their passengers may be landed on the Saltee Islands to observe flora and fauna.
"We have got to develop strategies to capture all of those possibilities," says Mr Cowman.
The whole pilotage network of the State is under general review at the moment, and a report to the Minister for the Marine is pending.