1930s, and 15 July 1935 The Palace on the hill, the airfield on the flatPalace na kopci, letisko na rovine

Under Czechoslovakia the spa was rebuilt to a modern standard, and the Palace — the large sanatorium that still dominates the terrace — went up on the hill in the 1930s. Down on the level ground by the river something quite different began: the first military aircraft landed at Tri duby on 15 July 1935, and a flying school opened there in May 1936. Both halves of modern Sliač, the spa and the airbase, were in place before the war started.Za Československa kúpele prestavali na moderný štandard a na kopci vyrástol v tridsiatych rokoch Palace — veľký liečebný dom, ktorý terase dominuje dodnes. Dolu na rovine pri rieke sa začalo niečo celkom iné: 15. júla 1935 pristálo na letisku Tri duby prvé vojenské lietadlo a v máji 1936 tam otvorili leteckú školu. Obe polovice moderného Sliača, kúpele aj základňa, stáli už pred vojnou.