Small Military Field Telegraph Set after restoration.
These Sets were made-up by Royal Ordnance Factories and a few commercial suppliers for use in WWI front-line Trench or Dug-out positions.
They used standard commercial components - Patt. 1056A Key, 300 Ohm Sounder and Lineman's Galvanometer (a modified "Detector, Q & I"). A carrying case would have been provided.
This example is unmarked as to origin, so is possibly an ROF product. The Key is by ATM Ltd. and dated 1916, the Sounder is by GPO and unmarked, but dated 1916 by a GPO QA stamp on the underside of the baseplate. The Galvanometer (not the original, but the correct type) is by Edison & Swan, also dated 1916.
The proper title of this instrument is the splendidly long-winded "Direct Working Single Current Intermediate Baseboard Set".