Fernando Gallego Herrera
Fernando Gallego Herrera (b. Villoria, Salamanca, 14 February 1901, d. Pamplona, 10 June 1973) was a Spanish inventor, engineer, and aviator.
In 1928 he presented to the government of Primo de Rivera the preliminary proposals for a 16 km tunnel under the Strait of Gibraltar between Spain and Morocco. It would be the basis of his 1928 patent "Float Inverted Gravity Foundation System". The tunnel had two double lanes for car traffic, two train tracks, and also four channels for drainage and a water level that regulated the lifting force.
See Spanish Wikipedia entry.
A 1930 description and illustrations in 'The Engineer' show the proposed tunnel as a buoyant concrete tube of oval section anchored to concrete caissons resting on the sea bed. 
-  The Engineer, 14 February 1930, p.185