The allies never took the submarine base in Lorient, and in fact, the French government tried to destroy the fortified base post-war but found the concrete largely impenetrable. The French used it as a sub base until the mid-90's and it's still open for tours today (I toured it about a decade ago).Fixed fortifications are not guarantors of victory, but they do help.
In 1944, 75,000 American troops attacked 45,000 German troops in the fortress port of Brest. After weeks of fighting and almost 10,000 killed and wounded, the Americans took Brest.
The German retained Lorient, St. Nazaire, Royan, Dunkirk, and some others.
The long duration of the fighting at Brest, the appalling cost led Ike to forego attempting the reduction of the other ports until May 1945.
Fixed fortifications did that.