Type VIIC Free-Flooding Vent Patterns

Diesel exhaust outlets

Type VIIs had two diesel exhaust outlets, located on either side of the hull casing, usually above the line of vents in the rear main group. As the war progressed, the design of these outlets changed. New boats were fitted with the latest style, while boats that were in service were modified with the latest style during refits.

The earliest style (which I have called style 1) was a circular outlet located along the line of vents in the main rear group. This style featured on the early VIIBs in the batches U 45 to U 55 and U 99 to U 102, but not on the VIIBs from other batches or any VIICs. These round outlets were modified on famous VIIBs such as U 47, U 48, U 99 and U 100 to the original VIIC oval outlet (style 2). Style 2, the style in the Revell kit, has a large oval hole above the line of vents. Other VIIBs such as U 73 were launched with style 2, and never had the round outlet (style 1) that was standard on the earliest VIIBs. All early VIICs such as U 69, U 94, U 96, U 201, U 332, U 352, U 402, U 552, U 556, U 564, U 581, U 617 and U 651 had style 2.








02: The holes pointed to with arrows are not free-flooding vents but one of the two diesel exhaust outlets. At least four styles of exhaust outlet can be seen in photos of VIICs.

On some U-boats, such as U 87, U 96 and U 552, a shroud (style 3) was added over style 2 at some stage in their careers. The shroud directed the exhaust gases downward so that the boat would be rendered less visually detectable. In 1942, U 751 had a shroud over the outlet, plus two holes beneath the shroud.

Then, at some stage beginning in late 1941 or so, boats coming down the slipways sported a new style of exhaust outlet. This outlet (style 4), which featured upon U 209, U 227, U 253, U 302, U 441 and U 704, had an almost rectangular shape with two squares below. The late VIIBs U 83 and U 86 also sported style 4. A lip was added at the top of some style 4 outlets to keep the exhaust smoke from rising up. In 1942 the last exhaust outlet (style 5) was introduced. This style had two horizontal bars positioned at an angle that directed the exhaust gases downwards. Style 5 featured on U 226 when it was launched on the 18th June 1942. It is likely that by the autumn of 1942 all new U-boats launched had style 5. All subsequent U-boats, including U 241, U 995, U 1003 and U 1305 sported this last style of outlet. It is important to remember that some boats had different styles of outlet at different times. For example, U 203 was retrofitted with style 4 at some stage prior to April 1943, having originally had style 2 when launched.