Yarmouth Castle continued to be an important military fortification, used both as a fortress but also as a transport hub and a stores depot.
The repairs recommended in 1599 were carried out in the first years of the 17th century and a further £300 was invested in Yarmouth Castle and nearby Sandown Castle in 1609, including adding two angular buttresses along the walls facing the sea.

A survey in 1623 by the castle's captain, John Burley, reported that the garrison comprised only four gunners and the captain, with the buildings in a "ruinous" state and the defences in need of repair; similar concerns were raised in 1625 and 1629.
Suggestions that a half-moon battery should be added to the defences were not progressed, but in 1632 the parapets were raised in height and further lodgings and a long room for stores were constructed within the castle.
Some of the stone used for this may have been reused from nearby Sandown, whose walls had been destroyed by the sea; before it was used at Sandown, the stone appears to have been taken from the local monasteries.

Civil war broke out in 1642 between the followers of King Charles I and those of Parliament.
Initially, Captain Barnaby Burley, a relative of John, and an ardent Royalist, held the castle on behalf of the King with a tiny garrison.
Burley negotiated surrender terms, including that he initially be allowed to remain in the castle with armed protection, and the castle remained in the control of Parliament for the rest of the war.
Early during the Interregnum it was decided to increase the size of the garrison at the castle from 30 to 70 soldiers, due to concerns about a potential Royalist attack from the island of Jersey.
Most of the soldiers lived outside the castle itself.
The annual cost of this force was around £78 and in 1655 the garrison was made smaller again to reduce costs.

When Charles II returned to the throne in 1660, he demobilised most of the existing army and the following year the garrison at Yarmouth was given four days notice to leave the castle.
The King announced that the castle's artillery would be sent to Cowes, unless the town of Yarmouth agreed to take over the financial responsibility of running the site themselves.
The town declined to do so, but Charles repeated the offer in 1666; this time Yarmouth seems to have taken action, appointing four soldiers for a garrison, although the town did not assign an officer to command them, or apparently make any repairs to the now dilapidated castle.

The Crown took over the castle again in 1670, and Robert Holmes, the new Captain of the Isle of Wight, had some of the guns brought back from Cowes to the castle.
The site was refortified and a new battery placed on the adjacent quay, but the older earthworks were demolished and the moat was filled in.
Holmes built a mansion for himself alongside the castle, where on three occasions he hosted the King.

In 1688, Charles' brother, James II, faced widespread revolt and a potential invasion of England by William of Orange.
Holmes was a supporter of James, but although he intended to control Yarmouth Castle on the monarch's behalf, the local inhabitants and the garrison at Yarmouth sided with William, preventing him from openly siding with the King.
Yarmouth Castle continued to be an important military fortification, used both as a fortress but also as a transport hub and a stores depot. The repairs recommended in 1599 were carried out in the first years of the 17th century and a further £300 was invested in Yarmouth Castle and nearby Sandown Castle in 1609, including adding two angular buttresses along the walls facing the sea.
A survey in 1623 by the castle's captain, John Burley, reported that the garrison comprised only four gunners and the captain, with the buildings in a "ruinous" state and the defences in need of repair; similar concerns were raised in 1625 and 1629. Suggestions that a half-moon battery should be added to the defences were not progressed, but in 1632 the parapets were raised in height and further lodgings and a long room for stores were constructed within the castle. Some of the stone used for this may have been reused from nearby Sandown, whose walls had been destroyed by the sea; before it was used at Sandown, the stone appears to have been taken from the local monasteries.
Civil war broke out in 1642 between the followers of King Charles I and those of Parliament. Initially, Captain Barnaby Burley, a relative of John, and an ardent Royalist, held the castle on behalf of the King with a tiny garrison. Burley negotiated surrender terms, including that he initially be allowed to remain in the castle with armed protection, and the castle remained in the control of Parliament for the rest of the war. Early during the Interregnum it was decided to increase the size of the garrison at the castle from 30 to 70 soldiers, due to concerns about a potential Royalist attack from the island of Jersey. Most of the soldiers lived outside the castle itself. The annual cost of this force was around £78 and in 1655 the garrison was made smaller again to reduce costs.
When Charles II returned to the throne in 1660, he demobilised most of the existing army and the following year the garrison at Yarmouth was given four days notice to leave the castle. The King announced that the castle's artillery would be sent to Cowes, unless the town of Yarmouth agreed to take over the financial responsibility of running the site themselves. The town declined to do so, but Charles repeated the offer in 1666; this time Yarmouth seems to have taken action, appointing four soldiers for a garrison, although the town did not assign an officer to command them, or apparently make any repairs to the now dilapidated castle.
The Crown took over the castle again in 1670, and Robert Holmes, the new Captain of the Isle of Wight, had some of the guns brought back from Cowes to the castle. The site was refortified and a new battery placed on the adjacent quay, but the older earthworks were demolished and the moat was filled in. Holmes built a mansion for himself alongside the castle, where on three occasions he hosted the King.
In 1688, Charles' brother, James II, faced widespread revolt and a potential invasion of England by William of Orange. Holmes was a supporter of James, but although he intended to control Yarmouth Castle on the monarch's behalf, the local inhabitants and the garrison at Yarmouth sided with William, preventing him from openly siding with the King.
Yarmouth Castle