The truck is typically not seen in normal gameplay because in order for the player to get near it, the player must use the move Surf. In order for the player to use Surf, he or she must have obtained the Soul Badge from Fuchsia City.
Normally, before the player can obtain the Soul Badge in Fuchsia City he or she must obtain a HM01 (Cut) from the captain on the S.S. Anne to teach Cut to a Pokémon and reach Lavender Town from Cerulean City. After the player receives HM01 (Cut) from the captain and leaves the S.S. Anne by walking it causes the S.S. Anne to set sail; preventing access to the Vermilion Harbor and the S.S. Anne truck without glitches.
There is no known reason for the truck's existence although some players think that it might be an Easter egg or a pre-release remnant.
Mew was rumored to be available by pushing the S.S. Anne Ship Truck with Strength, however this rumor was proven to be false (although such a trick is possible with arbitrary code execution and using Strength on the truck is a means of finding Mew in the ROM hack Pokémon TPP Red).
In later gamesIn Pokémon FireRed and LeafGreen the S.S. Anne Ship Truck returns and players can obtain a Lava Cookie nearby it.
In Pokémon XD: Gale of Darkness there is a hidden Easter egg referencing the truck by a Trainer known as Beauty Ogoin. Beauty Ogoin appears randomly on the normal setting in VS Mode Quick Battles and states prior to the battle, "There's no POKéMON under a truck, maybe you'll just find a MUK! Do you like it? I'm writing a song!" When she is defeated, her loss text is: "Aiyeeh! I can't battle as well as I write songs!".