The Ton-class minesweepers

Sea mines were a major threat to shipping during both World Wars, and during both conflicts the Royal Navy had hundreds of minesweepers in service. Some were specially designed and built ships, and some were merchant trawlers and drifters that were taken into service, often with their original crews.

In the period after the Second World War, the Royal Navy decided to build two classes of minesweepers for inshore and coastal work. The former were the Ham-class (and their related Ley-class) and the latter were the Ton-class.

A side view of the Ton-class minesweeper as designed,.

One hundred and nineteen Ton-class minesweepers were launched between 1952 and 1959, and they served in several navies besides the Royal Navy:

• Argentine Navy: Four ex-Royal Navy and two ex-Royal New Zealand Navy ships.
• Royal Australian Navy: Six ex-Royal Navy ships.
• Ghanaian Navy: One ex-Royal Navy ship.
• Indian Navy: Four ex-Royal Navy ships.
• Irish Navy: Three ex-Royal Navy ships.
• Royal Malaysian Navy: Seven ex-Royal Navy ships.
• Royal New Zealand Navy: Two ex-Royal Navy ships.
• South African Navy: Two built to order and eight ex-Royal Navy ships.

HMAS Curlew, the former HMS Chediston.

The class's characteristics were:

• Displacement: 440 tons
• Dimensions:
• Length: 152ft (46m)
• Beam: 28ft (8.5m)
• Draught: 8ft (2.4m)
• Propulsion: 2 x Mirrlees diesel engines (later 2 x Napier Deltic engines) each powering a propellor
• Speed: 15 knots
• Complement: 33
• Armament: 1 x Bofors 40mm anti-aircraft gun; 1 x Oerlikon 20 mm anti-aircraft gun or 1 x M2 Browning 0.5-inch machine gun

The hulls were built of two layers of mahogany on an aluminium fame, and as many fittings as possible were made of non-ferromagnetic metals in order to reduce  the ships' magnetic signature. Their shallow draft and small displacement gave them some protection against contact mines and pressure and mines and allowed them to operate in shallow inshore and coastal waters.

The ships were originally fitted with Mirrlees diesal engines, but these were replaced by Napier Deltic diesal engines. The latter were an opposed-piston, valveless, supercharged, two-stroke diesel engine that were designed to have a high power-to-weight ratio. The design was very effective and was employed in numerous small warships (e.g. Royal Navy Dark-class and Norwegian Tjeld or Nasty-class,fast attack craft) as well as British Railways Class 55 locomotives).

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Special mention should be made of two Ton-class ships, HMS Bronington and HMS Wilton:

• HMS Bronington was commanded by the-then Lieutenant Charles, Prince of Wales (now King Charles III) from February to December 1976. She is currently awaiting preservation.
• HMS Wiltonwas launched on 18th January 1972 and commissioned on 14th July 1970, and was a specially-built Ton-class minesweeper with a glass-reinforced plastic (GRP) hull. Most of her fittings were salvaged from the hull of HMS Derriton when the latter was scrapped. The experimental use of GRP proved successful, and the subsequent Hunt-class minesweepers were built with GRP hulls. She currently serves as a the floating clubhouse of the Essex Yacht Club at Leigh-on-Sea, Essex. 

HMS Bronington.