I found two mistakes in the following text :
Only one of the two main turrets had been fitted with the other (1) being loaded onto a transport ship which was sunk by a (2) U-boat .

1) A full main turret was impossible to load on a transport ship .The turret N°2 is anyway partially seen on the ship at his arrival in Casablanca . Because on draft problem in St.Nazaire it was decided not to install the four 380 mm guns on the ship . Each one had a weight of 100 metric tons and a lenght of 18 meters. It was ordered by Captain Ronarc'h to load them in the cargo "Mecanicien Principal Carvin " (a coal cargo) but the boom of the crane was to weak for this great load . Only 2 guns were loaded the two other ones being destroyed on the quay so the Germans would not use them .

2) This cargo went south until the entrance of the Gironde between Royan and Le Verdon and was sunk by the Luftwaffe . The wreck is still indicated on the maritimes charts .

Thank you alhanselmann. I have amended the article about Jean Bart and referenced this post as the source.