A fourth-rate was, in the British Royal Navy during the first half of the 18th century, a ship of the line mounting from 46 up to 60 guns. While the number of guns stayed subsequently in the same range up until 1817, after 1756 the ships of 50 guns and below were considered too weak to stand in the line of battle, although the remaining 60-gun ships were still classed as fit to be ships of the line. However, the 50-gun ship continued to be used largely during the Seven Years' War, and during the time of the American Revolution a whole new group of 50-gun ships was constructed, not for the battlefleet, but to meet the needs of combat in the shallow waters off North America where the larger ships found it difficult to sail. But by the French Revolutionary and Napoleonic Wars, even this function was in retreat, and few 50s were built. The 60-gun ships were also dying out, superseded initially by the 74-gun third-rates, although by 1793 there were still four 60-gun ships left in harbour service. The few 50s that remained were relegated to convoy escort, or as flagships on far-flung stations; a number were also converted to troopships, armed only "en flûte" (i.e., with most of the guns removed or stored below decks, to make more room for passengers or cargo).