This is one of six ratings (1st, 2nd, 3rd, 4th, 5th, 6th) in the rating system of the Royal Navy.

In the British Royal Navy, a fourth-rate was a ship of the line mounting 50-60 guns. Though used largely during the Seven Years' War, by the time of the American Revolution and especially the French Revolutionary and Napoleonic Wars, the fourth rate was considered too weak to stand in the line of battle. The few that remained were relegated to convoy escort, or as flagships on far-flung stations.

Some fourth rates did remain in active service even during the Napoleonic Wars, especially in the shallow North Sea, where the Royal Navy's main opponents were the Baltic powers and the Dutch, whose own fleet consisted mainly of 50 and 64 gun ships. However, HMS Leander, 50 guns, was with Horatio Nelson at the Battle of the Nile. As late as 1807, fourth rates were active in combat zones, illustrated by the fatal incident between HMS Leopard, 50 guns, and the US frigate Chesapeake, 38 guns, which almost precipitated the War of 1812 five years early!

The US's "44-gun" frigates (such as Constitution) in operational use were never armed with fewer than 50 guns, and were generally seen as equivalent to 4th raters.

Reference

• Rif Winfield, The 50-Gun Ship (Chatham Publishing, 1997) ISBN 1-86176-025-6 - A first-rate reference for everything about British fourth-rates.