It is a piece of military communication equipment from the mid-20th century.

The unit was designed to allow a second signal to be sent over the same line as a traditional telephone device which could be used

as a component of a Fullerphone, a device used for secure communication during

a fascinating example of early signal technology. This item is a rare find.

Size approx.; 4x4 inches.

I have others listed

It’s common today to send multiple signals over a single metallic or fiber optic line yet that technology was innovative in the late 1920’s

when it was applied to military line signaling.

The advantages were obvious: if one line could carry more than one signal, the resources and

manpower to string and maintain that line could be optimized while a greater number of troops could

communicate with each other. One such line sharing device the complicated ‘Superposing Unit 1 Transformer’.

The manual says the unit provides: Superposing a series Fullerphone on a telephone circuit,

Superposing a phantom to earth Fullerphone or telephone circuit to a twin line,

Superposing a Fullerphone or telephone phantom circuit on two twin lines,

Further developments of the phantom arrangement where possible and In cases of the above,

providing for an intermediate Fullerphone or telephone station on a phantom or phantom to earth circuit…which

suggests a large number of confused young signalers spent a great deal of time studying the use and operation of these units.

This extract was copied elsewhere just to give a general idea of the items use.