I was mesmerised by the cloud of glassfish that hung around me, clung to me really, in a gently pulsating mass. At the same time I was inwardly celebrating my total lack of decompression obligations – even though I had already spent the best part of an hour on a Red Sea wreck at 25m.

A totally silent interaction with nature and an hour’s bottom time at 25m, breathing a moist Nitrox mixture – this is the diving of the future. It’s not scuba, it’s ccuba: closed circuit underwater breathing apparatus.

More than half a century after Cousteau first opened a window on the underwater world for recreational divers, it is only now, with rebreathers, that the magical realm he famously dubbed The Silent World is beginning to live up to that name.

Anyone who has dived with open-circuit scuba knows how noisy it is listening to the sound of your own breathing.

I was testing the new Buddy Inspiration rebreather from UK manufacturer AP Valves, in Hurghada, Egypt. On one hand, it was an amazing experience. On the other, it was like learning to dive all over again. It was comical on day one to see a group of us, mostly advanced BSAC, TDI and PADI instructors with thousands of dives between us, struggling with our buoyancy and making the kinds of mistakes that our students normally make.

Using the Inspiration is not really that complicated. Yes, there are a few new rules to learn, but the main problem for experienced open-circuit scuba divers is that there are a lot of ingrained rules to unlearn.

Mastering buoyancy was the first problem. The unit weighs approximately 27kg, so if you are used to diving with aluminium 12-litre tanks and a 5mm wetsuit in the Red Sea (as is common) you can dispense with a lot of the lead you would normally use. I found that just one 2kg weight in a special pocket on top of the unit stopped it riding up in the water into a vertical position.

Most of us were grossly overweighted until we sorted it out. On land the unit is fairly bulky, but in the water it felt quite streamlined, especially when compared with its closest American counterpart, the CisLunar, which weighs twice as much.

Because you are on a closed circuit breathing loop, descending takes a bit of practice and you can no longer use lung-volume to control your buoyancy. You need to get air out of the wings-style BCD, your lungs and the counterlung, or breathing bag, to descend. Exhaling through your mouth doesn’t work; you need to exhale through your nose.

Then, as you start to descend, you have to add air to the counterlung by pressing an inflate button, similar to the inflate button on a drysuit, in order to breathe.

Again, with practice, you learn how to maintain a constant volume in the loop for ease of breathing. Repeated mask clearing – if you have a leaky mask – effectively turns the unit into a semi-closed rebreather (because you’re venting air into the water periodically) so it’s essential to have a well-fitting mask to avoid wasting your air (diluent).

The unit is mounted on your back just like a conventional scuba unit, but you have two 3-litre cylinders, one containing oxygen, the other diluent and a twin-hose assembly and mouthpiece like old-fashioned open-circuit rigs. As you breathe from the loop, carbon dioxide is removed by the scrubber unit which sits between the tanks – all housed in a stylish, yellow plastic fairing.

Setting up the Inspiration for diving needs a little more preparation than conventional scuba. First you need to check that the scrubber material – sofnolime – which filters out the carbon dioxide, is in good condition.

Next you turn on the two electronic handsets which control the oxygen levels in the breathing mix; the first is the master, the second is a back-up or slave. They run through a self-diagnostic check for battery level and calibration, reminding the diver of essential checks to make before asking: ‘Dive now?’ It’s virtually impossible to make a mistake in following the menu of questions and instructions.

Martin Parker, managing director of AP Valves, comments: ‘We are obviously looking at the leaking handsets problem, but the important thing is that the unit does tell you if there is a power problem.’

The main advantage of CCR is the use of a constant partial pressure of oxygen, which means the actual percentage of oxygen in the Nitrox mix is varying constantly with depth throughout the dive. At greater depths oxygen toxicity is kept at bay, and at shallower depths the mixture breathed is a progressively oxygen-rich one.