Planned as a replacement for the successful Letov S-328, the S-528 was a reconnaissance and light bomber aircraft. The structure of the S-328 was strengthened and the powerplant was upgraded to a 800 hp (597 kW) Gnome-Rhône Mistral Major. Due to the German annexation of Czechoslovakia, only six were built.
In March 1939, Germany occupied the Czech part of Czechoslovakia and Slovakia declared its independence. Consequently, Slovakia inherited a number of Letov S.328 reconnaissance and light bomber biplanes that had been based in its territory. Additional aircraft were obtained from German stocks acquired during its annexation of Czechoslovakia, as well as 50 new built examples.
On 23 March 1939, Hungary invaded Slovakia in the Slovak–Hungarian War (23-31 March 1939). During the conflict, Letov S.328s conducted reconnaissance and bombing attacks on Hungarian troops.
When Slovakia participated in the German invasions of Poland in 1939 and the USSR in 1941, the S.328s were again used for bombing and reconnaissance missions. They were later used on anti-partisan operation in Ukraine. Following the Slovak National Uprising in September to October 1944, up to 11 Letov s.328s were seized by insurgents.
Following the German occupation of Czechoslovakia in 1939, the Luftwaffe incorporated captured Š-328s into their inventory. The Letov Š-328 only saw limited use by the Luftwaffe during World War II, primarily as a trainer. A small number were also used in the night attack role on the Eastern Front in the Winter of 1942–43.
