Karel.
The engine telegraph system consist of the order telegraphs, e.g. the telegraphs setting the orders. You have two sets (port and stb) of telegraphs one set in the conningtower and one set in the control room transmitting the COs or officer of watchs order to the dieselengineroom or e-motor room.
The orders given can be both direction of propellerrevs and the speed. For the dieselengines on the VIICs built after 1942 there was no reversing hence the dieselengine telegraphs could only order ahead revs and speed. As can be seen on the image below the telegraph could order increase of revs by 10, diesel engine operation or e-motor operation as well as batterycharging. Maneuvring of uboats delivered later 1942, like alongside the jetty, you used solely the E-motors.
When the engine order is given by the CO or officer of the watch, the helmsman put the orderlever in the ordered position which is transmitted to the diesel engine- or E-room. Prior to the execution of the order the engineer answeres, acknowledges, the order by putting the lever in the same position as the orderlever and adjust the engine. Likewise in the E- room where the electricians carry out the order in the same way.
When an order is given, a sound is made and a red light is flashing only to be stopped when the oder is acknowledged by the engine telegraphhandle.
Tore