German U-Boat

U-Boat Bridge Conversions & Designs

U-Boat Bridge Conversions or Bridge Designs referred to the different bridge layout used by the Type VII U-boat during the war. In order to accomodate a variety of different anti-aircraft weaponry, the original bridge design was modified, giving rise to at least seven different bridge conversions during the war.

At the beginning of the war, the standard U-boat anti-aircraft armament is a single 20mm Flak intended as a defensive measure against aircraft. Mounted on the main upper deck, aft from the Bridge, this position limited the arc of fire due to the obstructing bridge. It was eventually relocated to a platform just aft of the bridge.

By mid-1942, the very rapid increase in hostile aircraft made it clear that the single gun was an inadequate defense against enemy air attacks. This gave rise to numerous bridge conversions to improve the boat's air defense capability.

Bridge Conversion I The original design sported a single 20mm mounted aft of the bridge on a slightly lowered platform. This platform became to be known as "wintergarten". The first improvement was the addition of two twin 15mm MG151 to the bridge. The MG151 was later replaced by twin Breda 13.2mm MGs.

Bridge Conversion II Two single 20mm Flaks were mounted, one on the bridge and one on a lowered platform aft (wintergarten). This was considered a stop-gap measure pending the arrival of twin 20mms.

Bridge Conversion III The Flak platform on the bridge was widened to accommodate two single 20mm Flaks to be mounted side-by-side. This conversion was applied only to the Type VIID.

Bridge Conversion IV Intended as the ultimate solution to the air threat, most Type VIIs carried this bridge design, which became mandatory for all operational boats from August 1943. This design consisted of two twin 20mm Flaks side-by-side on the bridge platform and either a quadruple 20mm or a single 37mm Flak on a lowered wintergarten aft of the bridge. The quadruple 20mm Flak was fitted with a protective shield. The two twin 20mm and single 37mm were later also fitted with protective shields.

Bridge Conversion V This was an extension of Bridge Conversion IV. An additional platform (wintergarten) was mounted forward of the bridge to accommodate additional anti-aircraft armament. Only one boat had this design, U-362.

Bridge Conversion VI Essentially the same as Bridge Conversion V, except the front wintergarten was slightly lowered and had open sides to improve underwater performance. However all the clutter on the boat’s deck had adversely increase hydrodynamic resistance. Only two boats had this design, U-673 and U-973.

Bridge Conversion VII Two flak platforms were mounted, one fore and one aft of the bridge. Each platform accommodated a twin 37mm Flak cannon.

Bridge Conversion VIII The final flak conversion which completely encircled the bridge. There were four platforms, one forward, one after, and two on each side of the bridge.

Undesignated Conversions A handful of boats were allowed to outfit their custom anti-aircraft configuration. These were non-official designs and were not widespread. PS:- High resolution Bridge Conversions are available in the exclusive section here.