The Royal Engineers' Air Battalion had pioneered experiments with wireless telegraphy in airships and aircraft before the RFC was created. Unfortunately the early transmitters weighed 75 pounds and filled a seat in the cockpit. This meant that the pilot had to fly the aircraft, navigate, observe the fall of the shells and transmit the results by morse code by himself. Also, the wireless in the aircraft could not receive. Originally only a special "Wireless Flight" attached to No. 4 Squadron RFC had the wireless equipment. Eventually this flight was expanded into No. 9 Squadron under Major Hugh Dowding. However, in early 1915 the Sterling lightweight wireless became available and was widely used. In 1915 each corps in the BEF was assigned a RFC squadron solely for artillery observation and reconnaissance duties. The transmitter filled the cockpit normally used by the observer and a trailing wire antenna was used which had to be reeled in prior to landing.