Гей ви Стрільці Січовії
Written in 1914 according to the 1918 Сьпіваник Українських Сїчових Стрільцїв.
There are conflicting sources about the origin of the melody song. Most Ukrainian sources attribute it as being based on an unnamed Magyar (Hungarian) melody (source) in WWI. However, Ciężkie czasy legionera (Polish Legionist Song) also sprung into existence in WWI (source) and is extremely similar, especially with the same "Раз два три" portion. The Polish version usually claims the melody is of Romanian origin (Śpiewnik Marszowy by jodla.org): "Słowa anonimowe, muzyka na podstawie melodii ludowej rumuńskiej. Pieśń szczególnie popularna w WP w II RP [WWI in the Second Polish Republic]".
Jak szło wojsko raz ulicą is another extremely similar Polish song, also from WWI (Source).
Dalej, bracia, równym krokiem is a third extremely similar Polish song, dated to March 1914, just before WWI (Source). This is credited as "Piosenka lwowskich legionistów", which suggests this might be the source of the Ukrainian one.
"Hej panienki posłuchajcie" is a fourth similar song ( https://www.youtube.com/watch?v=kEa500WYpnw )