The He 112 was to designed to compete for the RLM specification for a completely new monoplane fighter, a compitition that is surprisingly lost to the Bf 109 against which it proved more manoeuvrable. Seventeen were supplied to Spain where they were flown by civilian pilots and were judged superior to the Bf 109C. 15 of these aircraft continued in Spanish service until after World War II.
Luftwaffe test pilots were delighted with the aircraft and although a small run were built as insurance, Messerschmitt retained the overall contract. A number of these were later sold to the Japanese Navy which hated them because of the high wing loading. 13 B-0 and 11 B-1 models were sold to Romania which used them in the 1941 invasion of the Soviet Union.
http://www.warbirdsresourcegroup.org/LRG/he112.html