Submarines off Torre Del Mar??

We were recently on holiday in Torrox. One day we walked on the coast from Mezquitilla to Caleta, past the marina there. As we approached Caleta we spotted 5 strange craft in the water, off the coast of Torre Del Mar. They seemed very low in the water and stationary. At times they looked slightly below the water line with only a turret showing towards the rear of the centre of the craft.

As we walked on, they started moving towards Caleta, very slowly and never coming nearer to the coast and as we didn't have our camera or binoculars with us we couldn't make a record or investigate further. None of the locals seemed to notice them, but it was certainly something we have never seen before. At no point did they dive and they all moved in a slow formation. It was obvious no one was on the 'deck' and they looked too small to be  big submarines or anything.  They were all  black / very dark coloured.

Does anyone know what these might be? We wouldn't be the only ones who saw them. Maybe they're a regular feature?

Thanks in advance.
Paul & Lisa