30-pounder long gun

Installed on the lower deck of the larger warships from the 1820s, the 30-pounder long gun was the largest caliber used in the late Navy of the Age of the Sail, used on the ships defined by the Commission de Paris. On three-deckers, the middle deck used 30-pounder short guns, and the upper deck used 30-pounder carronades. The flagship Bretagne was an exception to this rule, retaining the older 36-pounder long gun as to maximise the weight of her broadside.

In the wake of the Napoleonic Wars, the French Navy undertook a number of reforms, most notably a reform in the artillery system. In contrast with the 1788 system, where large warships armed their main batteries with large 36-pounder long guns and upper deck with smaller long guns using smaller shots, it was decided to standardise on the 30-pound calibre, and deploy a variety of guns of different weights, as not to overload the tops. The differences in weight were obtained by fielding a large 30-pounder long gun, a shorter 30-pounder with a thinner barrel, and a 30-pounder carronade.

This allowed a much simplified handling of ammunition, and significantly increased the broadsides of warships. A first-rank 60-gun frigate of the 1840s thus armed had a heavier broadside than a 74-gun ship of the line of the 1780s.