A general term for all types of vessel used by lighthouse services.
The German term Seezeichenfahrzeug is a general term for all vessels that mainly attend aids to navigation in order to service them.
The English term servicing vessel is often used with this meaning.
Please note that this is the term as it stands in the original IALA Dictionary edition (1970-1989)
International Association of Marine Aids to Navigation and Lighthouse Authorities - AISM