Šajkaši (Serbian: Шајкаши, German: Tschaikisten or Nassadisten) were the river troops guarding the Danube and Sava, and especially, the Port of Belgrade, against the Ottoman Empire from the 16th to the 19th century. At the time, the rivers were borders of the Kingdom of Hungary and Habsburg Empire with the Ottoman Empire. They had special military status. Their name derives from the small wooden boat known as Tschaiken (Šajka), a type of galley.
A group of Serbian Šajkaši settled in Slovakia, where they continued their service, known in Slovak as čajkári.
The Šajkača hat is derived from the 18th-century Šajkaši