HMS Newcastle was a 50-gun fourth rate of the Royal Navy which saw service in the Napoleonic Wars and the War of 1812.

In 1603 all English warships with a complement of fewer than 160 men were known as 'small ships'. In 1625/26 to establish pay rates for officers, a six-tier naval ship rating system was introduced. These small ships were divided into three tiers: fourth-, fifth- and sixth-rates. Up to the end of the 17th century, the number of guns and the complement size were adjusted until the rating system was actually clarified. A 'fourth-rate' was nominally a ship of over thirty guns with a complement of 140 men.