The town of Yarmouth on the Isle of Wight may have been attacked by the French in 1543; if so, this raid probably encouraged the construction of a castle there as part of the second wave of Device Forts.[7][lower-alpha 1] The fort functioned alongside the existing defences in the Solent and protected the main crossing from the west side of the island to the mainland.[9] Yarmouth Castle was a square artillery fort built around a central courtyard with an angular, "arrow-head" bastion protecting the landward side.[10] It was initially equipped with three cannons and culverins, and twelve smaller guns, firing from a line of embrasures along the seaward side of the castle.[10] It was garrisoned by a small team of soldiers, consisting of a master gunner, a porter and 17 soldiers, commanded by Richard Udall, the castle's first captain.[11] Udall lived in the castle, but the soldiers resided in the local town.[12]