Zaha,
IMO Air would be OK for the exterior of HMS Repulse & penetration should be done on TriMix or HeliOx.
As for HMS Prince Of Wales(POW) ... TriMix or HeliOx should be the choice, exterior or penetration due to the depth & Low Viz.
The best will always be TriMix or HeliOx, as what you have mention.
FYI...Helium is expensive down here 

I knew that about helium is expensive.. I just think about narcotic at depth that all. I know many divers do it and done it, but if something happen well!!! bla bla bla.. but for new divers or new student who want to jump at Repulse with Air. I would say too risky.
Bro.. Diving suppose to be fun not suicide sports.! you know what i mean.
Why not just taking step by step, no rush.. That wreck ain't go no way!! taking proper course with proper gas not with AIR at that depth!!
MUW well know about safety diving forum all the member understanding about safety of diving, talk about safety, conservation, environment.. but if we didn't follow.. I just want o help our diving community going stronger and safer everyday.. that's all.
Safe Diving
Zaha
Syed: don't get mad at me..

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