The first three production Ju 188 E-1 machines were delivered with BMW engines in February 1943, followed by another seven in March and eight in April. A conversion testing unit was formed up in May and after testing were attached to an operational unit, with the first mission, an attack by three Ju 188E-1s on a factory in Lincoln, Lincolnshire taking place on 18 August 1943. By the end of the year, 283 Ju 188s had been delivered (including Ju 188Fs) and two new factories were added to the production effort. Most operational machines differed from the prototypes only in having a MG 151/20 cannon in the nose and dorsal turrets in place of the MG 131. The MG 131 I was intended to be used in the Ju 188 E-1 or the G-2 but the heavy armament in the A and E series was the MG 151/20. The Ju 188 E-2 was built as a torpedo-bomber but was identical to the Ju 188 A-3.