It seems to me that the best application for this would be in small, relatively self contained systems intended for very long submersion. I think an underwater dwelling or workshop would be cool - you could stick a team of SpecOps guys somewhere offshore and have them wait for… whatever. Or else have a team reach the shoreline and disappear - no submarine to track or boat to chase, and when you figure they’re long gone, they come back.

But new technology has a way of ending up in forms, and having effects radically different from what was initially envisioned.

SEALs and underwater EOD (mine clearance) use the latter. In the case of EOD, it’s because open circuit systems like SCUBA produce noise which you don’t want around acoustic mines (also, current rebreathers are nonmagnetic because guess what you don’t want to have around magnetic mines).

A gill based system probably would not replace the rebreathers unless it somehow avoided releasing exhaled gas into the water (and it’d have to go somewhere - you couldn’t store it on the diver because it would affect buoyancy). Also, you’d probably want a small bottle of nitrogen or other inert gas to mix with the oxygen because O2 is toxic at high concentrations. Breathing oxygen at a partial pressure of 2.0 (which you get with regular air at less than three hundred feet depth) will produce convulsions and unconsciousness - your mileage may vary. Regardless, having these things happen underwater will fatally kill you to death.

None of these musings in any way takes away my astonishment at thie line of research. If successful, it would be the greatest breakthrough in diving since Cousteau’s aqualung.

I’m not a diver myself, but it appears that, besides the obvious benefits to the diver, a tankless system would reduce the logistical support requirements for deployed diving detachments.

I suspect that the Navy is letting the Army foot the bill for this one, not to mention having to work out any bugs in the system.