Those of you down the Blue Lagoon a few weeks ago may have seen a strange sight. A group of experienced divers staring with all the bewilderment and excitement of Trainees on a Have-A-Go night. They are watching as an Instructor assembles a strange looking set of diving gear. Later you may have seen groups of three divers entering the water looking like overgrown turtles with a hard white shell on their backs. Were you unlucky enough to be the Dive Marshall you might have sworn quietly as you attempted to follow the lack of bubbles.

What you would actually have been witnessing was a group of MK and Dunstable divers having their first taste of diving with a re-breather. Read on for more information.

The day started with a briefing in the MK Clubhouse. Our Instructor, Andy Hetherton, introduced himself as the BSAC Southern Region Coach as well as an experienced nitrox, mixed gas and re-breather diver. His lecture, which lasted, about an hour and a half covered a number of interesting topics.

As with conventional SCUBA, there is much debate about exactly who invented the re-breather and when. Nonetheless, everyone agrees that re-breathers were around before conventional (or open-circuit) diving equipment. Re-breathers can use as little as 10% of the gas of normal diving and become more efficient at depth. It’s only in these modern times of twin fifteen litre cylinders and pony’s that divers have been able to be so wasteful with their breathing gas. The military have also given much pressure (no pun intended) to re-breather development as it is generally considered silly to sneak under an enemy ship leaving a trail of bubbles behind you.

Some of the different makes and types of re-breather were explained. These ranged from the Dràger we would be using (£2,500; Citroen 2CV equivalent) through the Buddy Inspiration (£3,700; XR3i) to some custom built American job (£12,500; Porsch 911 with go-faster stripes and fluffy dice).

Now over to the Bluey to assemble the kit. Having tried to lose the Instructor on the twisty drive from the Clubhouse, we wasted no time in assembling the first set of kit. Surprising for those who thought the whole point of a re-breather was a smaller, lighter, set of kit, the first thing to do was add 12 lB of lead to the backpack. Then came filling the "scrubber" with what our instructor described as "cat litter", checking the two breathing bags and the first and second stages and putting it all together. Our last task was to fill the four litre "main" cylinders by decanting from a fifteen litre cylinder of nitrox.

As we donned the kit, Andy explained the vital importance of "closing down" the mouthpiece before taking it out of your mouth. Unlike a normal DV, allowing water to enter the mouthpiece on a re-breather floods the whole system. This has two immediate effects, you lose a lot of buoyancy and you can’t breath any more!

And so at last into the water. There were so many odd sensations to describe that I can’t cover them all properly. Within seconds you noticed an eerie quiet since there was no rattle of bubbles as you exhale. A few seconds later, you hit the bottom in a cloud of silt and remembered the other thing Andy had said earlier. Since the air is being re-breathed from your lungs into a bag and back again, your buoyancy does not change as you breathe. Up to this point I had not realised how much we use our lungs for fine adjustment, oh well, a few ups and downs (in four metres) never hurt anyone.

The last thing I noticed was so obvious I didn’t realise till after the dive. When I dive, I am so used to being hit in the mouth by a blast of cold, dry air with every breath that I take it for granted. The re-breather delivers air which is slightly damp and warm, just like the air I am breathing as I write this. It is amazing how much warmer you feel on a dive, breathing warm air!

After sorting our buoyancy out, we went off for a gentle dive. This is where the title of this article comes in. Twenty minute dive to twelve metres with a cylinder size of four litres. Stop at several points to do different drills (close mouthpiece, remove from mouth, replace, open mouthpiece etc). Air in 80 bar, air out 60. We could well believe Andy’s claim that a small group of divers could do a weekends diving using just a single fifteen (between them) for top-ups between dives. Also remember that with a re-breather your air consumption at forty metres is the same as at six.

The final question I can hear you all asking; would I buy one? The answer is not yet. If I was an underwater photographer and wanted the lack of bubbles, I might be tempted. If I did a lot of long cold water dives, the warm air might encourage me. Until then, at a minimum of two and a half grand for the kit, another few hundred for the training (and the same again for my buddy) I’ll stick to my fifteen litre.