The Auxiliary Fleet ( Tren Naval in spanish ) comprises all minor auxiliary vessels, self-propelled or not, owned and manned by the Armada, that operate inside docks, ports, stations and naval bases, that have assigned support tasks for surface vessels and submarines.
Like in many other NATO navies, all units assigned to this force are marked with the letter Y ( stands for Yard ). Nowadays these units support management of training torpedoes, coastal mining, instruction duties and diving support, besides common logistic support duties.

Considering that information on the actual status of the auxiliary fleet is almost non-existing, the number of active units should be around 143.