K17 WWI

[Jose]

I've found in a spanish newspaper that in january 1916, one morning appeared on the sea (in Spain) an iron boat with the only indication "K17" on both sides, containing barrels of petrol and two british flags inside.

I've been searching and -in fact-, there was a british submarine K Class with that name, but it was build up and commisioned after january 1916. All K Class british submarines were built after january 1916 with no exception.

What could be the iron boat with K17 that the newspaper said?

Thank you very much.