In 1935, the Go 145 started service with Luftwaffe training units. The aircraft proved a successful design and production of the Go 145 was taken up by other companies, including AGO, Focke-Wulf and BFW. Licensed versions were also manufactured in Spain and Turkey. The Spanish version, called the CASA 1145-L actually remained in service until long after World War II.
Ignoring prototypes, 1,182 Go 145s were built in Germany for Luftwaffe service. An unknown number of license-produced Go 145s were also built. Further development of the aircraft was done. The Gotha Go 145B was fitted with an enclosed cockpit and wheel spats (an aerodynamic wheel housing on fixed-gear). The Go 145C was developed for gunnery training and was fitted with a single 7.92 mm (.312 in) MG 15 machine gun in the rear cockpit, requiring removal of that cockpit's flight controls.
By 1942, the Russians began using obsolete aircraft such as the Polikarpov Po-2 to conduct night harassment missions against the Germans. Noting the success of the raids, the Germans began conducting their own night harassment missions with obsolete aircraft on the Eastern Front. In December 1942, the first Störkampfstaffel (harassment squadron) was established and equipped with Gotha Go 145 and Arado Ar 66. The night harassment units were successful and by October 1943 there were six night harassment squadrons equipped with Gotha Go 145.
Also in October 1943, the Störkampfstaffeln were brought together into larger Nachtschlachtgruppe (NSGr) (night ground attack group, literally night battle group) units of either three or four squadrons each. In March 1945 Nachtschlachtgruppe 5 had 69 Gotha Go 145’s on strength of which 52 were serviceable while Nachtschlachtgruppe 3 in the Courland Pocket had 18 Gotha Go 145’s on strength of which 16 were serviceable. When the war in Europe ended on 8 May 1945 the Gotha Go 145 equipped the majority of the Nachtschlachtgruppen.