In February 1933 the Dornier Do 13 A, was introduced as a development of the Do 11. It had a rigid, fabric-covered fuselage and the same wingspan, 28m, as the Do 11 C. but used the Junkers double-wing flaps and ailerons and the Siemens Jupiter VI engine, later replaced by the more powerful BMW VI 7.3 ZU when it went into mass production. After a few problems had been overcome, production began in earnest. Mos Do 23 Fs were committed to training after the introduction of the Ju 86. Since it did not prove to be a suitable alternative, Dornier tried every possible improvement to the fuselage and wings to rescue the design. In September 1934 tests began on the much-modified aircraft, now designated Do 23 F. Further strengthening resulted in the Do 23 G production version, which, however, had a higher flying weight. Up to 1936 240 were produced by Dornier at Manzell and Wismar, and by Henschel and the Hamburger Flugzeugbau. This all metal aircraft was replaced as the standard bomber of the Luftwaffe by the Junkers Ju 86. The DO 23 was armed with three MG 15s, and a simple bomb sight was located in the nose.