The first phase of this work took place from 1539 until autumn 1540. The Moravian engineer Stefan von Haschenperg was responsible for the design of the fort, being paid the substantial salary of £75 a year for his work on this and other similar projects, including Calshot, Hurst, Sandgate and Sandown. Philip Chute, John Fletcher and William Oxenbridge, all prominent local men, served as the commissioners for the project, Oxenbridge becoming the pay master. Finding sufficient numbers of workmen was difficult and some had to be pressed into service unwillingly. More artillery pieces were sent to the castle ahead of the work being completed, and were probably installed in temporary battery positions around the castle site.