The Pen Men is a free model of a nuclear powered aircraft: the Charles de Gaulle. The Pen Men is not a real aircraft carrier, it's a 20 meters long (~65 feet) ship with a displacement of 20 metric tons. It was modelled after what will become the Charles de Gaulle.
The Charles de Gaulle is the only French aircraft carrier right now. Her design and construction were not without hiccups as it was delivered four years after her original due date. During the design phase it was decided to test the seafaring capability of the ship that was being drawn. And because computer assisted tools used in the naval industry were not powerful or complete enough in the 1980s to accomplish this task, a small model was built: the Pen Men.
The Pen Men was built in 1987 and went to be tested off the Lorient coast until 1991. Sea trials covered various aspects including manoeuvrability, speed and platform stability. The last one being crucial for flight operations. To accomplish the trials, the model was equipped with Magnus effect roller bearings to test an innovative stabilisation system, although this system did not make it into the actual Charles de Gaulle. A system of heavy charges on rails able to go from one side to another was preferred.
After its four years of good service, the Pen Men left the test dock in 1996 and is now on show on the Val-de-Reuil basin, which is a basin belonging to the French Navy. As of May 2021, the largest Val-de-Reuil basin (the B600, a 600 meters long basin) is used to test the future submarines of the Australian Navy [Update: The Australian Government preferred US nuclear submarines for its Navy and thus the tests in the B600 are no longer].