After graduation of art school Ruus joined Estonian Army serving in 10th Independent Infantry Battalion. On July 6, 1940 after finishing officer courses, Ruus was promoted to Sergeant and on September 8, 1940 he was assigned to a reserve unit.
Hando Ruus In Wehrmacht service
After Battalion "Narva" was ordered to be separated from Estonian Legion and united with 5th SS Panzer Division Wiking, Ruus was promoted to company leader where he led his unit in all battles that "Narva" was involved in, including the Battle of Izium and Battle of Cherkasy. In Cherkasy Ruus got wounded and was sent to Riga.
Battalion "Narva" was merged into the 20th Waffen Grenadier Division of the SS (1st Estonian) service and was sent back home, Estonia, where Estonian people welcomed them as heroes.
On April 1, 1944, Ruus married Salme Kurg.
On April 18, Ruus together with "Narwa" was sent to the border of Estonia fighting against advancing Red Army. Two days later he was promoted to SS-Obersturmführer (First Lieutenant). The Battalion had to fight along with Estonian 47th Regiment in the Battle of Auvere. On July 25, Ruus and his battalion had to hold back the onslaught of Red Army. Estonian positions were covered with Soviet artillery support. They launched ca. 80,000 shots but still their infantry was defeated back with great losses. Soviet Army lost about 8,000 men as killed, also 29 tanks and 8 planes
During the Battle of Tannenberg Line, Ruus became the commander of Battalion "Narwa", due the cause of all the other officers deaths.
Ruus also fought in the Porkuni. After fighting heavily Ruus and his battalion was cut off by Soviet troops and was taken prisoner. He also fell ill with pneumonia and he was sent to Gatchina, Russia. Later he was transported to Leningrad where he was presumably executed on March 31, 1945.
- October 29, 1939 - Private (Estonian Army)
- July 6, 1940 - Junior sergeant (Estonian Army)
- September 21, 1941 - Lieutenant (Wehrmacht)
- April 18, 1944 - SS-Obersturmführer (Waffen-SS)
- August 1944 - SS-Hauptsturmführer (Waffen-SS)