Like several other of their sets along the way, the RAF [Air Ministry = A.M.] had proven equipment which the Navy could use for comparable applications [aeroplanes/air stations] for the Fleet Air Arm. With a few Admiralty modifications the Navy got the equipment off-the-shelf and largely already de-bugged: ready to go!

This is how the Type 610 came about.  It was the Type 8D transmitter [A.M. Type T1154B] modified by the Admiralty to be CRYSTAL controlled and REMOTE controlled for keying CW, MCW and R/T circuits. Arrangement were also made for the transmitter to work into a remote quarter-wavelength vertical aerial fed by means of a coaxial cable.  The Auxiliary Crystal Drive Unit can have up to 12 crystals in place and by using the harmonics, can produced a possible 36 to 48 crystallised frequencies.

See this file for details about the Type 610 transmitter RAF TX 1154 TYPE 610 TRANSMITTER.pdf.   The associated Send/Receiver relay switch {TX and RX {?} off the one aerial] was not used and the Admiralty had re-engineered this switch to stay permanently in the 'send' position. The transmitter in outfit Type 610, was sited remote from the operating position.

The picture above is self explanatory and shows the plug-in Admiralty crystal box.

In this file we show the overall block diagram of the transmitter system. Note the two sets of land lines [microphone and Morse key] and the number of units marked AM as opposed the modifications marked AP 610.pdf