During WWII, it was vitally eccential for any partipisant to be able to rapidly set a reliable telephone connection in a field situation. In Wehrchmacht, it used to be done by the transmission units "Nachrichtentruppen".
The Sd.Ah.25 ( Anhänger für Feldfernkabel - one axled trailer for long distance field cable), was designed for transportation of four signal cable drums and a "Verlegewagen" (Laying Cart), and comprised an a closed box-like superstructure with folding top, mounted on the Anhängerfahrgestell A 1 - the standard single-axle trailer chassis produced for Luftwaffe before the war.
It was possible to lay cable directly from the towed trailer with a top speed of 10 km/h. The cable drum had to be mounted inside the trailer on special supports, and an operator could sit on the unfolded bench beside to operate the crank.
A Kfz.15 used to be used as a towing vehicle.
The Verlegewagen was used for manual laying of the cable, and consisted of a frame, an axis and two removable wheels. During transport, the wheels of the Verlegewagen were fixed on front wall of the Sd.An.25 superstructure, while its frame was stored inside the trailer.
The Verlegewagen also could be used in a static position, once the frame standing on its sliding extensions. Then, it was possible to roll up or unroll the cable, using the wheel fitted with its folding handle as a crank.
German Cable Drum with long-distance field cable (the "Feldfernkabel", or "Ff-Kabel"), had weight of 70 kg., and was to storage, transport and laying of the 250 meters of the cable.
It consisted of the drum core, the two outer disks with rubber bandage, and another disk as an intermediate wall, separating the larger space for the cable from the smaller space used to accommodate the plugs and equipment.
Connecting multiple cables was possible over a distance of 50 km.
It can be increased up to a maximum of 120 km. by the use of intermediate device amplifying the signal, so called "Verstärkerspule" or "Pupinspule" (from the name of his hungarish inventor, Mihajlo Pupin).
Such a device was supplied wit each FF-Kabel Drum.
The Verlegewagen & Feldfernkabel are available separately as Lw35208 and Lw35207kits.