The radio room was installed forward of the control room in a dedicated cabin. There were multiple radio apparatuses: a radio transmitter (300 to 2,500 meters), a radio receiver (300 to 10,000 meters), a short-wave radio transmitter capable of 400 watts (15 to 60 meters) and a receiver for the same frequencies.
VELELLA was equipped with an announcing system. Each compartment could communicate with a central station located in the control room via a speaker microphone system. The internal telephone system had only four stations.
As already said, VELELLA was equipped with a klaxon operated from the control room. Upon sounding the alarm, all hatches would be secured and the engineers would commence the diving procedures, securing the diesel engines' intake and exhaust valves.
This submarine was equipped with two buoys situated on deck and attached to a retrieval system. If necessary, the buoys could be released and floated to the surface, giving surface units a telephone connection to the submarine.
There was a hydrophone system connected to external transmitters. The system was of domestic production and considered effective.
VELELLA was equipped with a gyrocompass installed in the auxiliary room which had three repeaters installed in various compartments (and also in the wheelhouse). There was also a magnetic compass installed in a waterproof casing on deck with a repeating station in the control room.
The gyrocompass received its directive from a high-speed spinning gyroscope driven by electric motors. Its directive action is based on the mechanical laws governing the dynamics of rotating bodies. When any object is spinning rapidly it tends to keep its axis pointed in the same direction. The gyrocompass consists of a spinning gyroscope, made north seeking by placing a weight below the axis, which is mounted in gimbals so that the movements of the submarine do not effect its position. A dial mechanically connected to the gyrocompass has the points of the mariner's compass marked on it and indicates the submarine's true course. The gyroscope required some time before becoming operational, thus it had to be started in advance of leaving port.