The class consisted of three ships, and were of composite (wood on metal frames) construction. They were based on the same basic hull as the and the . They had a large superstructure with an open bridge on top. The engines were up-rated to 1400bhp. They were crewed by 5 officers and 34 ratings, with accommodation on board for 4 officers and 18 rates.
In the late 1960s, two Ham-class minesweepers, and were rebuilt as inshore survey vessels very similar to the Echos, although they could be identified by having an enclosed wheelhouse and a tripod mast. They were renamed HMS Waterwitch and, respectively.
All ships were sold out of service in 1985. The Marine Society acquired two of the three vessels circa 1985 and converted them to training vessels. They were modified, from plans loaned by the Port of London Authority who had already purchased HMS Polsham in 1967 and converted her to a survey vessel, Maplin. The two vessels were renamed, Jonas Hanway and Earl of Romney, and were initially based and operated in conjunction with the Gravesend Sea School on the Thames at Denton. The third vessel is thought to have been included within the disposal package by the Ministry of Defence and acted as a spare parts source for the two operational vessels. Jonas Hanway was sold to a private owner in 1998 and is moored near Southend on Sea.[2]