External Reference

Date 1996

Event ID 585268

Category Documentary Reference

Type External Reference

Permalink http://canmore.org.uk/event/585268

The disadvantages of operating this exotic vessel are described on the basis of her single operational patrol (off northern Norway). The torpedo tubes were modified to fire British torpedoes and the valves were adapted to hydraulic working, rather than the manual working of German practice; many of the instruments retained their German labels and were calibrated in metric units.

German U-boats were designed to operate further from their bases than their British counterparts, being longer-ranged, deeper-diving, faster and more robust, with a consequent reduction in surface stability and crew comfort. Living conditions were primitive in the extreme and surface stability notably lacking, making surface watchkeeping uncomfortable. Crew efficiency deteriorated noticeably after about three weeks.

The surface speed of a U-boat was about 19kts, some 4kts faster than the British equivalent. Surface buoyancy was also reduced. The German high capacity batteries and MAN aluminium alloy engines had a comparatively short life, the batteries requiring annual replacement as against the British practice of having them last the life of the boat. Their diesel engines were, however, reversible. The electrical system was particularly complicated, while air bottles and fuel tanks were mounted outside the pressure hull. It was German practice to fit twin rudders for extra manoeuvrability and to use steel for periscopes and propellers, both being lighter and stronger than those in British service. U-boats never had a tight stern gland so their deep bilges needed constant pumping. Most U-boat machinery was mounted on buna (ersatz rubber). These differences provided enough spare weight to allow the use of steel 7/8in (22mm) thick for the hull, as against the 5/8in (16mm) of British practice.

Although the battery plates were replaced, the lack of compatible spares brought the operational use of this boat to an end. She was used for training and experimental duties in the Clyde before an unsuccessful attempt at a refit (in July 1943) resulted in her being taken out of service.

The capture of the vessel is also described, the name HMS/M Graph being taken from the code-name of the operation to recover the vessel from Canada to Britain.

P Durham 1996.