In 1747, the French dispatched a vital convoy of thirty merchantmen to carry reinforcements and supplies to their troops in North America. They were being protected by a small naval force, including four ships of the line. On the 14th of May, off Cape Finisterre in Spain, the convoy was intercepted by a much larger British force detached from the Channel Fleet. The French warships fought bravely to protect their charges, but outnumbered as they were, they were decisively defeated.
This minor action might have gone unnoticed by all but a few naval historians, were it not for the fact that it was the first time that the British encountered a new type of warship. The Royal Navy had considerable difficulty in defeating one of their French opponents in particular. It was a large two-decked ship of the line called Invincible that proved particularly troublesome. She put up such heroic resistance that at one stage she was engaged by no less than six Royal Navy ships. The Invincible was one of a revolutionary new French design that was soon to dominate the navies of the world. Like all ships of the time, she was identified by the number of guns that she carried, which was 74.
The British commander, Admiral George Anson, was very impressed with the captured French prize. He wrote about her in glowing terms to the Board of Admiralty, comparing her with his own flagship, the 90 gun, second rate, Prince George. The Invincible was seven feet longer, two feet wider and had had almost 200 tons more burden. Despite only having two gun decks, instead of the three that his ship had, and eighteen fewer cannon, she packed a much greater punch. This was because, for reasons of stability, ships with multiple gun decks could only carry light cannon high up. The extra guns on the Prince George’s upper deck added little to her firepower, and this contribution was more than outweighed by the greater number of heavy pieces carried on the Invincible’s lower decks.
But it was not just her cannon that impressed Anson. With only two decks, the French 74 had a much lower, sleeker profile than his towering flagship. This made her more manoeuvrable and stable. She was faster, too, and carried her lower deck guns higher above the surface of the sea. He deduced that this could prove a vital advantage in a fleet action fought in poor weather, when ships like the Prince George might not be able to open their lower deck gun ports at all. His recommendations were clear. In this new French ship, Anson had seen the future. The Royal Navy’s battle fleet should be built around 74s. When he became First Lord of the Admiralty in 1751 he was able to put this into practice.
So what was so special about this new type of ship? The Invincible, and all the 74s that came after her, were the perfect balance of size, sailing qualities and economy. The ultimate arbiter of the outcome of naval battles in the latter half of the 18th century was the 32 pounder cannon*, known in the Royal Navy as “ship-smashers”, and 74s were big enough to carry these guns. Smaller ships than 74s existed, but they could only carry, at best, lighter 24pdr cannon on their lower gun decks, and as the century progressed they slowly disappeared from the line of battle.
Larger ships than 74s could, and were built, but these were disproportionately more expensive to construct. A wooden ship has many parts that have to be made from a single piece of timber, such as the knees that hold up the decks. The larger the ship, the harder (and more expensive) it becomes to source these components. Three-decker warships also tend to be less stable and slower than those with two decks. They still had a role to play, particularly as flagships, with their additional space to accommodate an admiral and his staff, and extra firepower to protect them. At a time when the navies of Europe had to operate in all weathers and on the distant fringes of their expanding empires, it was weatherly 74s that were sent out to defend their nation’s interests.
When the Invincible was captured in 1747 there was not a single 74 in the Royal Navy. By the end of the century three quarters of British ships of the line were 74s, and some actions, like Nelson’s victory at the Battle of the Nile, were exclusively achieved with these ships. The Invincible’s descendants had become the backbone of all the major navies of the world.
*36pdr in the French and Spanish navies