Abstract: The apparatus is intended for vertically linking a first chain and a second chain under water. The apparatus is characterised in that it comprises a lower base (1) with an open cross-shaped slot (5) into which the last link of the first chain (6) is inserted, extending above said lower base (1), while a guide/holder (2) for the second chain (7) is attached to the lower base (I) over said slot, said guide/holder containing an H-shaped shackle (II) that is coupled to the last link of said second chain (7) by means of a first bolt (12), the last link of the first chain (6) being inserted in the free space in the shackle (11) so that both chains (6-7) are coupled by means of a second bolt (13).