Medically the Rouses died of Decompression Sickness (DCS) as a result of them ascending too fast and forgoing their mandatory decompression. But that isn't their real cause of death. Their real cause of death is their lack of training, preparedness, and experience. Almost anyone can be on a dive boat and do a technical dive, but it is just a game of Russian roulette. The rouses were playing with their lives and ultimately paid the price for it. They had very little experience in the deep technical diving of the north Atlantic with less than 500 dives each they did not posses the bank of knowledge required to deal with rescue and self rescue scenarios under these conditions. Furthermore, they had no experience on U-boats whose claustrophobic confines are much smaller and harder to navigate than normal shipwrecks. They should have performed many dives on shallower U-Boats such as the U-352 to gain experience in these settings. Lastly they were breathing air which is cheaper and easier to use then Heliox but makes one susceptible to Nitrogen Narcosis which would ultimately lead to the situation within the wreck. In conclusion, The nitrogen narcosis and DCS were not the route cause of this disaster. The Rouse's inexperience, lack of training, and lack of preparedness lead to the situation that ended in their untimely deaths.