Marine (military)
In the earliest days of naval warfare, there was little difference between sailors and soldiers on a warship. The oarsmen of Ancient Greek and Roman ships had to be able to fight the oarsmen of other ships. Armed soldiers were used on Greek ships to get on board enemy ships to fight their crews. The Roman Navy's two legions, I Adiutrix and II Adiutrix, were among the first special naval infantry units.