An IMO (International Maritime Organisation) number is a unique identifier that is given to all ships when they are constructed. When you complete your ENS you need to provide the IMO number of the vessel that you will be travelling upon. It is imperative that the IMO number that is submitted on the ENS matches that of the ship that you will be travelling on. Failure to submit a correct declaration will slow down your journey and prevent you from travelling until all of the documentation is completed correctly.