BREST, LORIENT, SAINT NAZAIRE, LA ROCHELLE AND BORDEAUX, ALL THE MAJOR FRENCH SUBMARINE PENS WERE AT GERMAN CONTROL FROM JUNE 1940. FROM THEN ON A MASSIVE UBOAT OPERATION AGAINST ALLIED MERCHANTS IN THE ATLANTIC ENSUED AND HAD HEAVY LOSSES TO ALLIED MERCHANT NAVIES, THE MAIN BURDEN BEING SUSTAINED..