Besides the trawlers, a number 01 other vessels are employed on the routine sweeping of the War Channel : the motor minesweepers, which have a displacement of about 200 tons, used mainly to sweep ground mines in the shallow waters of river estuaries and port approaches ; the whalers, many of which burn oil fuel, a matter of importance when a small crew is required to steam the ship on a long passage ; and the drifters, which in peace-time fish for herring with drift nets, their size making them handy ships for sweeping in confined areas.

These vessels are not usually employed in clearing extensive minefields laid outside narrow waters, a duty which is the function of the fleet minesweepers.

In the earlier days of the war the auxiliary paddle-sweepers were used for clearances. 1 n fair weather a well-trained flotilla would carry out this work satisfactorily, but the paddlers' radius of action was limited, the risk of damage to their paddle-wheels made them particularly vulnerable, and when mined they were difficult to keep afloat, so that as more fleet sweepers came into commission they were relegated to other, but no less useful, duties.

The fleet sweepers do not belong to the Royal Naval Patrol Service, but are R.N. or " General Service " ships, and are classed as " major war-vessels." The oldest type is the Albury class, laid down towards the end of the last war, and named after inland towns in Great Britain—Pangbourne, Derby, Ross. They have a displacement of 710 tons, a speed of 16 knots, and are the only coal-burners left in the Royal Navy : hence their nickname of" Smoky Joes."

Next come the Halcyons, named after minesweepers of 1914, somewhat larger and faster than the Alburys, while the new Al-gerine class is the largest and fastest of all. Between the two are the modern Bangors, called after British ports, which have been encouraged to adopt the ships of their own name, send them comforts and books, and