One Junkers W 34 be/b3e managed to break the then-current altitude record on 26 May 1929 when it reached 12,739 meters (41,795 feet).

The total production numbers for the civil market were around 1,000, a further 2,024 his and haus were built under license for the RLM and Luftwaffe.

The Junkers K.43, nicknamed the "Bush Bomber", was used extensively during the Chaco War (1932–1935) fought between Bolivia and Paraguay.

In 1930 Finnish Air Force bought a single W 34 (JU-122) for maritime operations and six K 43s (JU-123 – JU-128) for use as light bombers, during Continuation war the planes were used as transports, evacuating wounded and supplying Long-Range Recon Patrols behind the enemy lines.

Additional five W 34s were bought in 1944 for radio navigation training (JU-131 – 135), after the war Finnish Border Guard operated the remaining planes until 1950.