Canal defense light, a British secret weapon intended to illuminate and dazzle german troops in night attacks with the use of its extremely powerful searchlight located in the turret. Originally mounted on Matildas, later on grants which could retain their 75's with the light in a dummy turret. Its secrecy hampered its deployment; its most notable use was late in the war defending the Ludendorff bridge over the Rhine from enemy frogmen. This is somewhat ironic, as the name "canal defense light" was just a cover to keep the nature of the project secret, but in the end it really did become an armored searchlight defending riverine infrastructure.