Guglielmo Marconi (S 521) was a Sauro-class submarine of the Italian Navy.

[1] Guglielmo Marconi was laid down at Fincantieri Monfalcone Shipyard on 1 July 1976 and launched on 20 October 1979.

She was commissioned on 6 November 1982.

She is currently moored at Quay Sauro Calata San Vito, pier 2, north side in the La Spezia Naval Base.

[2] Gugliemo Marconi was sold for scrap 2023.