Signals units operated wireless and telephone equipment to allow the various parts of the army to communicate with each other in the field. Divisional signals units contained three or four companies/squadrons, depending on the type of division, with a total strength of about 28 officers and 700 other ranks. Four main types of wireless sets were used in action. The 18 set, usually used for signals between company and battalion headquarters, weighed about 30 lbs and had a maximum range of five miles. The No. 38 had a shorter range, about 2 miles, weighed somewhat less, and was used within the company and for communication with supporting tanks. Both were typically carried in a pack by the infantry. The No. 19 and 22 sets, meanwhile, had longer ranges and were fitted into vehicles such as tanks or universal carriers. The No. 19, used by armoured units, had three channels: the A set for communication with headquarters, B for use between the four tanks of a troop, and C for internal communication within the tank. Finally, the No. 22 set was similar to the No. 19 with slightly longer range and was usually used between formation headquarters or in artillery units.