This was intended to engage enemy ships with catapults and possibly early cannon, and incorporated the local chapel of Saint Petroc within its walls.

The castle saw service during the English Civil War of 1642 to 1646, during which its vulnerability to attack from the land became apparent, resulting in the Gallants Bower defensive work above it being used to provide additional protection.

After years of neglect in the early 19th century, the castle was upgraded in 1859 with modern artillery, but defending the port of Dartmouth was no longer a military priority.

[1] By the 12th century, the town's harbour, located in the estuary of the River Dart, was an important trading and fishing port, able to hold up to 600 vessels.

[3] By the 1370s, during the Hundred Years War, Dartmouth was a key target for the French navy and the Crown repeatedly advised the town to improve its defences.

[4] Nothing was done, however, until in 1388 John Hawley, the mayor of Dartmouth and a privateer, was authorised by Richard II to raise funds from the town for a new "fortalice by the sea" to defend the harbour.

[6] It was constructed on land in the manor of Stoke Fleming, belonging to the Carew family, lent by them due to the threat of French attack, and was built around a pre-existing chapel to Saint Petroc on the site.

[7] It held catapults to attack enemy ships, and may also have been armed with early cannon and equipped with a chain to block the entrance to the harbour.

[8] It did not see active service, but may have deterred the original plans of the French and Breton attack force in 1404, which, under the command of Tanneguy du Chastel, landed at Slapton Sands instead, where they were then dispersed by the local militia.

[15] Despite Henry's initial successes, France and Spain made peace in 1544, leaving England exposed to a French invasion, backed by her allies in Scotland.

[18] Sir Peter Carew, a soldier and the local Member of Parliament for Dartmouth, opposed this final addition, arguing that it trespassed on the family's house within the castle.

[19] A law case followed, and in 1554 the town regained the property after Carew fled the county facing charges of treachery; he returned in 1556 and retook the castle.

[20] Two years later, Hortensio Spinola, a Spanish spy, described the castle as being defended "with 24 pieces and 50 men", commenting that the harbour was well protected and that the inhabitants were "warlike".

[36] The introduction of shell guns and steam ships during the 1840s created a new risk that the French might successfully attack along the south coast, and fears grew of a conflict in the early 1850s.

[37] Further worries about France, combined with the development of rifled cannon and iron-clad warships, led to the Royal Commission on the Defence of the United Kingdom being established in 1859, and expressing fears about the security of the south coast.

[39][40] It was manned by three professional soldiers, and a team of over fifty-five reservists, drawn from the newly formed Sixth Devonshire Artillery Volunteer Corps.

[41] The castle, however, was of low military priority, only of importance because the harbour might be used to as a staging post to attack Plymouth, and the guns allocated it were old-fashioned.

[47] On the north side of the site is the main gun tower, looking out across the River Dart, and Saint Petrox Church; to the south-east is the Old Battery, facing out to sea.