Toilet sinks Submarine – FMEA could have saved lives

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Adam Bahret

I was recently doing an FMEA with a team and an engineer asked for an example of a product failure where an FMEA would have benefited the program. One example that always comes to mind is the U-boat 1206. Twenty-four days before the end of WWII it sunk 8 nautical miles off the coast of Scotland, all because the toilet was flushed incorrectly. Here’s the story…
U-1206 was a Nazi submarine fitted with new deep water high-pressure toilets. This allowed them to be used while running at depth. Flushing these facilities were complicated and special training was required. Being able to flush at depth is a significant advantage for a sub because coming to the surface risked being sighted by a patrol and sunk. So this toilet was a major milestone in stealth technology in 1945.
On 14 April 1945, 24 days before the end of World War II, while U-1206 was cruising at a depth of 200 feet (61 m), 8 nautical miles (15 km; 9.2 mi) off Peterhead, Scotland, misuse of the new toilet caused large amounts of water to flood the boat. According to the Commander’s official report, while in the engine room helping to repair one of the diesel engines, he was informed that a malfunction involving the toilet caused a leak in the forward section. The leak flooded the submarine’s batteries (located beneath the toilet) causing them to release chlorine gas, leaving him with no alternative but to surface or the crew would be poisoned by the gas. Once surfaced, U-1206 was discovered and bombed by British patrols.
This sequence of events seems like a very obvious area of design concern when looked at from a system level. A deep water high-pressure toilet is a complicated new technology (High Risk), the toilet failure mode is to leak (Low detectability before event), a toilet on top of battery packs and wet battery packs will poison crew and the submarine will have to surface (High Severity).
One of the greatest values of an FMEA is multiple disciplines coming together to speculate about critical failure modes from a system perspective. It would be very easy to imagine in an FMEA the hydraulics engineer being asked what could go wrong with the plumbing system. His response would be “The toilet could leak if this very complicated flushing procedure isn’t done correctly” “What would you rank likelihood for this?” “It’s a complicated procedure, so I would give it a high ranking”. How about severity? I’m pretty sure the electrical engineer would have chimed in at this point about the batteries getting wet, chlorine gas, and the high possibility of fatality if they didn’t surface immediately. As well as this defeating the entire intent of the toilet reducing surface/visible time of the sub. By the end of the FMEA this would have been assigned a high severity, high likelihood and the whole scenario would have risen to the top of the list when the issues to address were being ranked by Risk Priority Number (RPN)
We will never know if the electrical engineer and hydraulics engineer ever even sat in the same room. The electrical engineer of course knew that water on the batteries would create a deadly gas, but did he know that a new, highly likely to leak, invention had just been put above it? Did the hydraulics engineer know that his new technology was in one of the most “critical leak” spots in the sub?

So a new highly complicated device was created so that the submarine did not have to surface and risk exposure to patrols as frequently. The deep water high-pressure toilet failure created a more critical scenario where surfacing had to be done immediately, unplanned, during critical stealth maneuvers. A tragic result from a lack of System’s Engineering.

FMEA’s were first created and used in the late 40’s by the US military. There must have been many examples like this to discuss when there was time to reflect on engineering process in peacetime.

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