War ships are untradeable rare items. They spawned in two out of 100 random locations in every world. When picked up by a player, it would immediately spawn in another location.
Note that once all these items have been distributed, you will be able to obtain them again during the corresponding holiday period.
A war ship could be taken from the table next to the Birthday gift during Old School RuneScape's first and second birthday in the city of Prifddinas and Varrock.