Three submarine cables testing keys, from left to right:

Reversing key, for testing purposes. Maker unknown, the brass levers are used to apply a continuous polarity to line.

“Saunders” type key to test capacitance in submarine cables,.

Made by Muirhead and Co. and used by Italcable , Montevideo.

“Rymer – Jones” discharge key, single pole, to test capacitance, made by Telegraph Works, Silvertown, London.