The roof is 26 feet (8 meters) tall with four layers of reinforced concrete, granite, more concrete, and steel. They wanted it impenetrable to aircraft, and given the shape it's still in, after 13 aerial bombing attacks and 70-plus years that goal seems to have been achieved.
For decades, the pens and the area around it were either vacant, or just for industrial use. Now the area is well developed, renamed Ville-Port, and there's a cafe, a night club, the museums, and across the street, a mall with restaurants and shops.
After making my way through a dark and narrow passage between two pens, I exited to this in shock. A massive cruise liner! It took me a moment to realize it was a trick of lighting and mirrors, and was just a small segment. Inside is a separate exhibition called Escal'Atlantic about the many incredible ships of this type built in Saint-Nazaire.
Not surprisingly, those engines got replaced only a few years after launch. Three new SEMT Pielstick 12 PA4-185 V12 diesels were installed, each producing around 952 hp each. They'd need to run every 5 days for roughly 5 hours to keep the batteries charged.
Very few submarines that you can tour have ladders, especially in the middle of the sub. (Health and safety concerns.) But while in the Espadon's ops you can climb up a few rungs to have a look in the sail. The big tube houses one of two periscopes.
The port of Saint-Nazaire was the location of what's called The Greatest Raid of All, a daring and flat-out incredible attack by the British on the only drydock outside of Germany large enough to repair the Tirpitz and Bismark battleships. The entrance to the Normandie dock, as it's called, is on the left here (it was filled with water during my visit, so not much to photograph). The mid and rear of the the destroyer HMS Campbeltown would have been visible in the center of the frame had this photo been taken that next morning. On the far right is Old Mole jetty, the planned escape route.
From the roof of the fortified lock, you can see the art installation called Suite de Triangles, by Felice Varini. This is the only location where they all line up in a row like this. Some triangles, on the other side of the port, look heavily distorted from any other viewpoint. The top of one triangle could be on a completely different building. You can get an idea what it looks like in the Google Maps overview or this short video.
If you're fascinated by WWII history, a tour of western France is a must. The sub pens here for sure, with the Espadon as an added bonus, but of course the beaches of Normandy, with the Redoutable as an added bonus.
The tour of the sub is 10 euros ($11USD/£8.50/AU$15.50), but there are other tours in the area, including Airbus, the shipyards and more, but most require booking well ahead of time.