Junkers J-4

The Junkers J.I (manufacturer's name J 4) was a German "J-class" armored sesquiplane of World War I, developed for low-level ground attack, observation and army cooperation. It is especially noteworthy as being the first all-metal aircraft to enter mass production; the aircraft's metal construction and heavy armour was an effective shield against small arms fire over the battlefield.

It was an extremely advanced design for the period, with a single-unit steel "bathtub" running from just behind the propeller to the rear crew position acting as armour, the main fuselage structure and engine mounting in one unit.

The J.I was well liked by its crews, although its ponderous handling earned it the nickname "furniture van". The aircraft first entered front service in August 1917. They were used on the Western Front during the German spring offensive of 1918.

The aircraft could be fitted with two downward-firing machine guns for ground attack but they were found to be of limited use because of the difficulty of aiming them. The J-Is were mainly used for army co-operation and low-level reconnaissance. They were also used for dropping ammunition and rations on outposts that could not be easily supplied by other means.

The production at Junkers works was quite slow because of poor organization and only 227 J.Is were manufactured before production ceased in January 1919. At least one was lost to ground fire, shot down by a French anti-aircraft machine-gun firing armour-piercing rounds, although this was apparently an isolated event as some sources claim none were lost in combat. Some were lost in landing accidents and other mishaps.