The Marder

The inability of the Neger to submerge made it very vulnerable to attack. The Marder was the succession of the Neger in which a diving tank was added in front of the cockpit which enabled the craft to dive up to a depth of 10 meters. The craft was slightly lengthened in order to accommodate the diving tank.
Although it was an improved version of the Neger, the Marder still suffered from two main disadvantages. First, underwater mobility was extremely poor and constantly required the pilot's full attention to maneuver the craft. Second, the lack of a periscope meant that it was virtually blind underwater. The pilot still had to surface to find his way and a submerged attack was not possible.
Very few attacks involving Marders were carried out. They were used against US warships in the Gulf of St. Tropez in the Mediterranean, but the mission was a dismal failure. There were also plans for U-997 a Type VII U-boat to transport these Marders for an attack against Russian warships in Murmansk, but owing to technical difficulties, the mission was called off. About 300 Marders were built.