The Royal Navy, commonly the Royal Yugoslav Navy, was the naval warfare service branch of the Kingdom of Yugoslavia. It was brought into existence in 1921, and initially consisted of a few former Austro-Hungarian Navy vessels surrendered at the conclusion of World War I and transferred to the new nation state under the terms of the Treaty of Saint-Germain-en-Laye. The only modern sea-going warships transferred to the new state were twelve steam-powered torpedo boats, although it did receive four capable river monitors for use on the Danube and other large rivers. Significant new acquisitions began in 1926 with a former German light cruiser, followed by the commissioning of two motor torpedo boats (MTBs) and a small submarine flotilla over the next few years. When the name of the state was changed to Yugoslavia in 1929, the name of its navy was changed to reflect this. In the late 1920s, several of the original vessels were discarded.

The Yugoslav Army, commonly the Royal Yugoslav Army, was the land warfare military service branch of the Kingdom of Yugoslavia. It existed from the Kingdom's formation in December 1918, until its surrender to the Axis powers on 17 April 1941. Aside from fighting along the Austrian border in 1919 and 1920 related to territorial disputes, and some border skirmishes on its southern borders in the 1920s, the JV was not involved in fighting until April 1941 when it was quickly overcome by the German-led invasion of Yugoslavia.