[3] Having competed independently in the Cantabrian Regional Championship, in 1946 they were promoted to the third tier of Spanish football, the old Tercera División, for the first time; the following campaign, they faced the biggest local club Racing de Santander (or Real Santander as they were known at the time), Rayo being relegated and Racing promoted.

[2] They went on to spend 20 consecutive years at the third level, coming close to promotion on a few occasions,[2] also performing the important task in developing young local players, some of whom (including Paco Gento, Marquitos, Ico Aguilar, Pedro Zaballa, Vicente Miera and Nando Yosu) went on to great success.

[2] Further elite players produced via a spell in the team included Tuto Sañudo, Juan Carlos, Manolo Preciado, Pedro Munitis and José María Ceballos.

[4] In 1993 the original Rayo was dissolved in a national move to formally absorb affiliated teams into the professional clubs' structure, and Racing de Santander B took its place.

[3] A new Rayo Cantabria, who started playing as an independent club in the regional leagues from 1993,[4] was also affiliated to Racing for four seasons, from 2003–04 to 2006–07.