Drug Trafficking Interdiction Assistance Act of 2008 - Amends the federal criminal code to impose a fine and/or prison term of up to 15 years for the intentional operation of, or for embarking in, any submersible or semi-submersible vessel that is without nationality (as defined by federal law) and that is navigating or has navigated into, through, or from waters beyond the outer limit of the territorial sea of a single country or a lateral limit of that country's territorial sea with an adjacent country with the intent to evade detection.
Directs the United States Sentencing Commission to amend or promulgate sentencing guidelines to provide adequate penalties for such offense.