The Fuller phone was invented in WW1 around 1915 by an officer called Fuller. It solved the problem of interception of telephone calls by the Germans. The calls were then secure unless intercepted using another Fullerphone. Needless to say these phones were closely guarded as a great deal rested on their security.
The Fullerphone was so successful it carried on in service through WW2 where improvements increased the Mark numbers. This version is a 1944 dated MkV complete in original wooden box as issued. Used condition. Not known if working. Photo shows actual item.