We're in 1870 to 1900. The breakthrough of electric engines, the first time a battleship is torpedoed by a submerged submersible and true submarine frenzy in France. With the efficacy of submarine attack now proven by the CSS Hunley, French and Spanish inventors further improved submersibles. France especially was in the vanguard of submarine development, realizing it had found a possible weapon against the hegemony of the British navy. Still, some problems continued to elude engineers...

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The Isaac Peral submersible: https://bit.ly/3z08sDV

On the Ictinéo I & II: https://bit.ly/3hovVsB

The Gustave Zédé: https://bit.ly/3tutUQq