Coastal convoys around Britain

Were trawlers useful only in coastal waters, and why did Britain's coastal convoys matter to the Battle of the Atlantic?

Larger trawlers did cross the Atlantic, but their coastal work was especially important because cargo still moved around Britain by sea through confined routes exposed to submarines, E-boats, and aircraft.

Ocean cargo often moved from Liverpool into coastal convoys serving ports around Scotland, the Irish Sea, Cornwall, and southern and eastern England. Shipping remained more efficient than rail or road for much internal movement, so the Atlantic supply line continued beyond the first British port. These predictable routes faced German coastal submarines, Schnellboote, and aircraft. Some coastal passages were more dangerous than the open ocean, where convoys had room to disperse.