A transporter erector launcher (TEL) is a Missile vehicle with an integrated prime mover that can carry, elevate to firing position and launch one or more missiles. Such vehicles exist for both surface-to-air missiles and surface-to-surface missiles. Early such missiles were launched from fixed sites and had to be loaded onto trucks for transport, making them more vulnerable to attack since once they were spotted by the enemy they couldn't easily be relocated, and if they were it often took hours or even days to prepare them for launch once they reached their new site.