But what the Rouses died of, it doesn't even matter if a chamber was on board. The book and an article I read said only a 400 ft deco would have worked (among other things)...
That is inconsistent with my experiance. U-869 at 230' is in about the same depth as the Doria at 240'. You have to remember the ratio of bubble compression. That is why treating hits from 200'+ dives are often in a chamber at 60' -- mostly US Navy Tables 5 & 6, but also others.
There are two major issues involved, diluent gas bubble compression (often immediate relief) and removal from the blood stream. Compressing the bubble about a third (60') will often restore most blood flow and high PPO
2 (pure oxygen) removes it from the blood very rapidly (2.82 ATA). It is very unusual that chamber DCS treatments for military or commercial HeO
2 dives below 300' treat deeper than 165'.
There are standard Navy treatment tables for 165' and deeper, but it usually means much lower treatment PPO
2 (air). Recompressing to 165' would drive the vast majority of diluent gas back into solution from a 230' dive. All the chambers I have worked with were rated to 300' pressure-equivalent, though rarely had the treatment gasses required below 225'.
The Rouses may well have ended up on a 165' or even 225' table, but 400' would not have made any difference. Granted, there is a lot we don't know about explosive decompression outside of animal studies (thankfully), but rapid recompression would have improved their odds of survival by many many times.
Why don't we use com gear? The last dive speaks over and over about if everyone simply had com gear most accidents wouldn't occur. ...
Lots of reasons. Wireless comms required for Scuba were almost unavailable then and are only marginally reliable now. It also requires a FFM; which seriously complicates gas changes, use of backup regulators, and the added dead air space increases CO
2 build-up. Surface supplied divers don't face these problems. Communications are hard-wired, they can use free-flow to clear CO
2, and gas changes are managed for them on the surface.