Some images of the wreck of HMHS Britannic. Titanic's unfortunate sister ship

Not entirely true. You will not be positively buoyant at a depth of 500m (or however deep this wreck is - I do not know) due to the atmospheric pressure, nor will you be able to dive this deep due to oxygen narcosis and the pressure of the water above you ‘pushing you down’. If you are positively buoyant using a BCD (buoyancy control device), then you can ascend. However you would not be able to dive as deep as this wreck without being inside a pressurised containment (submarine). If you are diving at a depth of, say 30m, then you could become positively buoyant by inflating your BCD with some air. However the more you ascend, the more air you will have to expel from your BCD due to the air expanding from ascending to a lower pressure. If you were to simply ‘swim up’ whilst overly buoyant, then you risk an uncontrolled rapid ascent which will cause the bends. This is why you wear weights combined with a BCD so that you can control your buoyancy. If your point is that you can just ‘swim up’ without having any overhead obstacles, then yes, you will be in less danger than cave diving where you cannot ascend to the surface in an emergency.

Source: Open water diving certified (a rookie ;)

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