They were of composite construction, that is, wood and non-ferrous metals, to give a low magnetic signature, important in a vessel that may be dealing with magnetically detonated mines.

They displaced 164 tons fully laden, were armed with a Bofors 40 mm gun or an Oerlikon 20 mm gun and were powered by a pair of Paxman diesel engines.

[1] The class shared the same basic hull as their inshore minesweeper counterpart the Ham class and the Echo-class inshore survey craft.

Unlike traditional minesweepers, they were not equipped for sweeping moored or magnetic mines.

This was a new role at that point, and the class was configured for working in the shallow water of rivers, estuaries and shipping channels.