|WARNING TELEPHONE OR WaT|
As a title, and bearing in mind that we are on a W/T Branch site, this looks in keeping, and it is obviously something to do with W/T....but the 'a' ?
So what is a warning telephone. Simple. A ships tannoy system. Over the tannoy came spoken orders, pipes, bugle calls, action station clangers/sirens, oh and yes, warnings. Wa/T was a course syllabus entry for the W/T branch and ratings were examined for higher rate on the various fits in the Fleet. It is not a subject which is even worthwhile describing, because although a very necessary part of a warship's organisation, a tannoy is a tannoy whether it is large or small and once you have heard one, you will know that it is usually very loud, very clear, an bloody annoying.
There were several Wa/T Sets [the 401, 402, 403 and 405] each one designed for a certain class of ship depending upon how many decks, how many compartments, and the size of the ships company. Based on those criteria, the 401  was fitted in certain battleships, cruisers and aircraft carriers. It covered five groups of loudspeakers viz, officers quarters, engine room group, crew spaces, communication group and the armament group. The system covered the VOICE facilities and the ALARM facilities. The 402, also a big ship system had more gadgets on it than on the 401. When the 403 was rolled-out in 1930, it was considered suitable for fitting into many types of ships and being more modern in design and manufacture it required a cabinet half the size of the earlier fits.
All Wa/T fits, including this, the Type 403, had a switch which when made, sent out a distinctive low tone to forewarn all, that a tannoy broadcast would be made shortly afterwards. With the Type 405 designed in 1936, this switch was not fitted, and as a HISTORY POINTER for you all, that was the start of the famous naval cry.
a warning message sent out before each and every NON-ROUTINE use of the Tannoy System. The 405 also introduced automatic gain control [AGC] which with better power amplifiers and speakers, gave a more easy to listen to quality. All ships in their turn were fitted with the Type 405 system.
Now just in case you can't read what is on the inside of the cover to the TALK BOX of the Type 405, here is what it says