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A Brief History Of Sidemount

From sumping through Wookey with a pair of repurposed, WWII Bomber O2 tanks filled with air; to wearing side mounted, bailout rebreathers enabling explorers to logistically conduct lengthly sub-100 meter cave penetrations. And let’s not forget the “Reccies” making holiday sidemount dives in Bonaire. It’s fair to say that sidemount diving has come a long way over the last half a century. Here is a brief history supplemented by talks by Lamar Hires, Bill Rennaker and Patrick Widmann. Grab two singles and dive in.



Adapted from Wikipedia and YouTube resources by InDEPTH. Special thanks to Michael Thomas for the historical CDG images.

One of Mike Boon’s original sidemount cylinders that was recovered from Sump 9 in Swildon’s Hole cave in 1972. He was actively exploring the cave in 1962.  The cylinder is now mounted on the wall of the Wessex Cave Club. The cylinder was obtained from the Ministry of Defense after WW2. It was originally an oxygen cylinders on bomber aircraft during the war.

The Beginning: UK Sump Diving

The idea of mounting cylinders on the diver’s chest and sides, originated from cave diving in the UK, during the 1960’s. During the original explorations of Wookey Hole, or other cave systems, explorers encountered submerged passages (sumps) that created an obstacle for further exploration. To bypass these sumps, they started bringing basic scuba equipment specifically to progress beyond the -mostly short and shallow- submerged areas. However, because these caves were mostly very confined spaces, and also because most of their exploration was primarily through the dry parts of these cave systems, their original needs were met with great success using small, minimalist configurations, which reduced bulk and weight that needed to be carried along.  

British cave explorer Mike Boon (1941-2014) , is generally credited with being the first cave diver to mount his diving cylinder on his side rather than his back to explore sumps in the early 1960s. Boon also advocated using only 1/4 of one’s air supply for the inwards dive reserving 3/4 for the exit and any emergencies. This pre-dates the modern thirds rule which is usually attributed to Sheck Exley. Photos courtesy of the Wessex Cave Club .

This early implementation of sidemount allowed cylinders to be easily transported individually, but also easily removed and replaced, therefore allowing these explorers to retain the ability to squeeze through the tightest restrictions. The remoteness of these submerged areas, and the nature of these dives -done often in very silty sumps- did not call for the need of perfect buoyancy control or efficient  propulsion techniques. Only the minimum needed equipment was carried. A mask, cylinder, regulator, method of attaching the cylinder to the body and on rare occasions a set of fins. Some of these early explorers started using a sturdy belt, with attached cam-band. That made it possible for a cylinder to be carried alongside the side of their body. With this system they could walk or even crawl through the dry cave sections, preserving a reliable and safe method of cylinder attachment when dealing with the submerged areas. Trim efficiency, reduced water resistance and buoyancy control were not taken into much consideration due to the morphology of those systems. This approach to the sump kind of cave exploration was generally called the English System at the time.

The Evolution (1970’s, Florida)

During the 1970’s the original English system was adopted by American based cave explorers, primarily in Florida.The Florida caves were mostly flooded systems and involved prolonged diving, thus more focus was needed to be paid towards developing the diving performance of the system, in particular buoyancy and trim. Divers required proper buoyancy control devices for extended time therefore moving the cylinders from the thigh, up towards the armpit. These explorers were the original cave divers as we know today. They started making their own home-made gear. Modifying off-the-shelf diving equipment, and creating new configurations from scratch. Most of their creations were using webbing harnesses and improvised bladders for buoyancy.

Telford Springs 1988 Woody Jasper. Photo by Tom Morris

The First Commercial Rig (1990’s)

In the mid-1990’s Lamar Hires designed the first commercial side mount diving system which was then manufactured by Dive Rite. It focused on the newly released Transpac harness. Even with a “proper” option available in the market, many cave divers continued to manufacture their own DIY configurations. At this time, the use of sidemount was used only by a small number of exploration-grade cave divers.

Mark Long and Wes Skiles 1996

Cave Diving Becomes Popular and with it So Does Sidemount (2000’s)

Brett Hemphill designed the Armadillo Sidemount harness in 2001. This innovative system brought several new features that would be used in many future sidemount designs. To name a few: BCD inflation was now located at the bottom of the harness instead of the top, butt-anchoring rear attachment pad, cylinder bungee attachment, bungee straps used for faster location of primary bungee. The widespread popularity of sidemount did not truly emerge until the mid-2010s though, when a parallel growing popularity of technical and cave diving started seeing the benefits of what it could offer. Spreading mouth to mouth but also for the first time because of the internet, sidemount was offering an alternative approach that mimicked a Hogarthian minimalism and functionality style, but with the added advantage of comfort, trim control and even if it was not accepted by everyone as a valid argument at the time, safety.

But there was no way to stop the wave that was coming, and was coming hard towards the calm diving waters. An unstoppable increase in interest for sidemount diving “motivated” many manufacturers -and some brilliant individuals- to design and sell their own versions of sidemount systems. OMS, Hollis and UTD developed equipment, while Steve Bogaerts released the incredibly popular, minimalist Razor system which became an instant game changer. With Razor we also saw for the first time, training aimed at a specific diving rig.

2006 Sidemount and CCR Bailout systems merge

The Rise of Sidemount Closed Circuit Rebreathers (CCR) (2010’s – today)

Even if Sidemount was not anymore a cave-only strict configuration, a great deal of it was still used primarily in overhead diving (cave and -more recently- mine diving). It was no surprise that after having found a solution with it to push through restrictions along the way, cave divers now needed the gas to reach further. The time for sidemount rebreathers had come. Initially faced with issues of breathing resistance, among others, CCR manufacturers started developing multiple units. The most popular design consisted of a unit worn on one side of the diver with the diluent on the opposite side. But competition brought innovation, and today we have a variety of different configuration options when it comes to Sidemount CCR. Divesoft introduced the Liberty Sidemount version, a fully autonomous unit, just slightly longer than an s80 cylinder, that includes diluent and oxygen cylinders in one compact design loaded with tech. KISS, after the success of the Sidekick, revolutionized design with the Sidewinder, the first unit that was worn “on top” of a complete Open Circuit Sidemount configuration, adding the benefits of CCR to it. And the list goes on.

YouTube: Lamar Hires – The History of Sidemount Diving (2017)

Lamar Hires of Dive Rite is considered to be one of the pioneers of sidemount diving. In this hour-long presentation, Lamar talks about the history of sidemount, how it came to be, and its evolution over the past two decades.

YouTube: Sidemount and Cave Diving History with Bill Rennaker and Lamar Hires (2018)

On October 27nd, 2018, Bill Rennaker and Lamar Hires were kind enough to talk to a group of cave divers at NFSA event and speak about the history behind sidemount diving and cave diving. The purpose of this video is to catalog and preserve the history of these prominent explorers. Part 2 will be posted soon.

YouTube: Sidemount History From The POV Of Patrick Widmann (2020)

Patrick talks about the history of the Sidemount Diving and shares his experiences which ultimately lead to the creation of the xDeep Stealth 2.0.

Please take a minute and complete our new: Sidemount Diving Survey. We will report the results in a coming issue.


Outside MagazineDeeper by Bucky McMahon. To the peerless Moles, practitioners of the gloomily claustrophobic sport of freshwater spelunking, the ultimate accomplishment is finding a virgin cave (1996) Sidemount – History of the Diving Equipment Configuration

Wikipedia: Sidemount Diving

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InDEPTH’s Holiday Rebreather Guide 2023

Making a list. Checking it twice. Gonna find out which breathers are naughty or nice. That’s right! It’s time again for InDEPTH’s Holiday Rebreather Guide. This year, we are featuring 32 models of back, sidemount and chest mounted rebreathers, including five new units for your shopping enjoyment. So, get out your Pre-Buy Checklist, and that Gift Card (you do have a gift card don’t you?!?), and buy the breather of your dreams. Ho, ho, hose!




by Michael Menduno, Amanda White and Kenzie Potter. Holiday images by Jason Brown, BARDO CREATIVE.

A Guide to Backmount, Sidemount and Frontmount Rebreathers

6 Dec 2023 – Ho ho ho! InDEPTH’s Holiday Rebreather Guide continues to pick up steam (machines). This season we added Mares Horizon semi closed rebreather and Lombardi Undersea Research’s new RD1 back mounted oxygen rebreather. We also added Lungfish Dive Systems “Lungfish,” And iQSub Technologies’ new FX-CCR front mounted breather along with the Flex2 sidemount CCR. As such we believe the Guide is the most complete one on the market! Pst, pst Mr. Scammahorn, are you still there? Happy shopping divers! Ho ho hose!

Remember you can find all of the Rebreather Forum 4 presentations here on REBREATHER FORUM 4

1 Dec 2022 – Ho ho ho! Once again, we have updated InDEPTH’s Holiday Rebreather Guide adding two new rebreathers; the new Gemini sidemount, needle valve mCCR from Fathom Systems, and the Generic Breathing Machine (GBM) front mounted, needle valve mCCR, with a dive computer-compatible, solid state oxygen sensor from Scubatron. We also updated the features on the Divesoft Liberty sidemount, and the JJ-CCR. This year, Vobster Marine Systems was acquired by UK-based NAMMU Tech, which plans to rename and re-issue a version of the VMS Redbare. See link below.

Finally, Innerspace Systems’ founder Leon Scamahorn agreed to work on getting us the needed information to add the storied Megalodon to the Guide. Scratch last year’s coal, Xmas cookies for you Mr. Scamahorn! Happy holidays shoppers, here is our updated rebreather guide! Mind those PO2s!

17 Dec 2021 – Ho Ho Ho! We have updated our Holiday Rebreather Guide with new rebreathers and updated features. Despite repeated requests, the only major closed circuit rebreather we are missing is Innerspace Systems’ Megalodon and its siblings. Tsk, tsk Leon Scamahorn, you’ve been a naughty boy! Behold, here is our updated guide. Mind those PO2s!

Dr. Bill Stone’s manned trial of F.R.E.D. at Wakulla Springs (1987). Photo courtesy of the US Deep Caving Team

However, it took the fledgling tech community at least a decade to adapt mixed gas technology for open circuit scuba, including establishing the necessary supporting infrastructure, which was the first and necessary step in the move to rebreathers. A little more than a decade after Stone showcased FRED, British diving entrepreneur Martin Parker, managing director of then AP Valves, launched the “Buddy Inspiration,” the first production closed circuit rebreather designed specifically for sport divers, earning him the moniker, the “Henry Ford of Rebreathers.” [The brand name later became AP Diving] KISS Rebreathers followed a little more than a year later with its mechanical, closed circuit unit, now dubbed the KISS Classic. The rest as they say, is history, our history. 

Buddy Inspiration advertisement from 1998. Courtesy of AP Diving.

Today, though open-circuit mixed gas diving is still an important platform, rebreathers have become the tool of choice for deep, and long exploration dives. For good reason, with a greatly extended gas supply, near optimal decompression, thermal and weight advantages, bubble-free silence, and let’s not forget the cool factor, rebreathers enable tech divers to greatly extend their underwater envelope beyond the reach of open circuit technology. 

As a result, divers now have an abundance of rebreather brands to choose from. Accordingly, we thought it fitting this holiday season to offer up this geeky guide for rebreather shoppers. Want to find out whose breathers are naughty or nice? Here is your chance.

Your Geeky Holiday Guide

The idea for this holiday guide was originally proposed to us by Divesoft’s U.S. General Manager Matěj Fischer. Thank you Matěj! Interestingly, it doesn’t appear to have been done before. Our goal was to include all major brands of closed circuit rebreathers in back mount and sidemount configuration in order to enable shoppers to make a detailed comparison. In that we have largely succeeded. We also included Halcyon Dive Systems’ semi-closed RB80 and more recent RBK sidemount unit, which are both being used successfully as exploration tools. 

Absent are US-based Innerspace Systems, which makes the Megalodon and other models, as well as Submatix, based in Germany, which manufactures the Quantum and sidemount SMS 200, neither of which returned our communications. M3S, which makes the Titan, declined our invitation to participate, as they recently discontinued their TITAN CCR—they will be coming out with a replacement unit, the TITAN Phoenix CCR in the near future. We did not include the MARES Horizon, a semi-closed circuit rebreather that is aimed at recreational divers. No doubt, there may be brands we inadvertently missed. Our apologies. Contact us. We can update.

Update (22 Jul 2021) – French rebreather manufacturer M3S contacted us and sent us the specs for their updated chest-mounted Triton CCR, which are now included in the guide.

Update (9 Dec 2020) – Submatix contacted us and the Guide now contains their Quantum (back mount) and SMS 200 (sidemount) rebreathers. We were also contacted by Open Safety Equipment Ltd. and have added their Apocalypse back mounted mechanical closed circuit rebreather. We will add other units as they are presented to us by the vendors. 

It’s The Concept, Stupid

The plan was to focus on the feature sets of the various rebreathers to provide an objective means to compare various units. But features by themselves do not a rebreather make. As Pieter Decoene, Operations Manager at rEvo Rebreathers, pointed out to me early on, every rebreather is based on “a concept,” that is more than just the sum of its features. That is to say that the inventors focused on specific problems or issues they deemed important in their designs; think rEvo’s dual scrubbers, Divesoft’s redundant electronics, or integration of open and closed circuit in the case of Dive Rite’s recently launched O2ptima Chest Mount. Shoppers, please consider that as you peruse the various offerings. My thanks to Pieter, who helped us identify and define key features and metrics that should be considered.

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Though not every unit on the market has been third-party tested according to Conformitè Europëenne (CE) used for goods sold in the European Union, we decided to use CE test results for some of the common feature benchmarks such as the Work of Breathing (WOB), and scrubber duration. For vendors that do not have CE testing, we suggested that they use the figures that they publicize in their marketing materials and asked that they specify the source of the data if possible. As such, the guide serves as an imperfect comparison, but a comparison nonetheless.

Santa’s Little Helper: Meet Rufus, BARDO’s Chief Muse Officer (CMO)

Also, don’t be misled by single figures, like work of breathing or scrubber duration as they serve only as a kind of benchmark—there is typically a lot more behind them. For example, whether a rebreather is easy to breathe or not is a function of elastance, work of breathing (WOB) and hydrostatic imbalance. In order to pass CE, the unit must meet CE test requirements for all three issues in all positions from head down, to horizontal trim, to being in vertical position (Watch that trim!), to lying on your back looking upwards. It’s more difficult to pass the tests in some positions versus others, and some units do better in some positions than others. 

The result is that some of the feature data, like WOB, is more nuanced than it appears at first glance. “The problem you have is people take one value (work of breathing for instance) and then buy the product based on that, but it just isn’t that simple an issue,” Martin Parker explained to me. “It’s like people buying a BCD based on the buoyancy; bigger is better, right? Wrong! It’s the ability of the BCD to hold air near your centre of gravity determines how the BC performs. With rebreathers you can have good work of breathing on a breathing machine only to find it completely ruined by it’s hydrostatic imbalance or elastance.”

Due to their design, sidemount rebreathers are generally not able to pass CE requirements in all positions. Consequently, almost all currently do not have CE certification; the T-Reb has a CE certification with exceptions. However, that does not necessarily mean that the units haven’t been third-party tested. 

Note that the guide, which is organized alphabetically by manufacturer, contains the deets for each of their featured models. In addition, there are two master downloadable spreadsheets, one for back mounted units and one for sidemount. Lastly, I’d also like to give a shout out to British photog phenom Jason Brown and the BARDOCreative Team (Thank you Georgina!), for helping us inject a bit of the Xmas cheer into this geeky tech tome [For insiders: this was Rufus and Rey’s modeling debut!]. Ho, ho, hose!

With this background and requisite caveats, we are pleased to offer you our Rebreather Holiday Shoppers’ Guide. Happy Holidays!!

Note – Most prices shown below were specified by manufacturer before tax.

Backmount Rebreathers

* In 2005, AP Diving launched its Vision electronics with In-Plane Switching (IPS) which enhances colour and visibility
**Typical scrubber duration using AP Tempstik increases practical duration to more than double CE test rate figures – as the AP Tempstik shows scrubber life based on actual work rate, water temperature and depth.
*** The work of breathing is the effort required to push gas around the breathing circuit BUT that figure alone is meaningless without knowing two other parameters: Hydrostatic load and elastance. Note that AP Diving rebreathers meet the CE requirements in all diver attitudes for both Hydrostatic Imbalance 0 degrees (horizontal, face down) and Hydrostatic Imbalance +90 degrees (vertical, head up.)
**** APD’s handset offers a “dual display” feature showing data from both controllers on the same handset. The user can also see the gradient factors chosen and the mVolt outputs of the cells by holding a button down.
* Divesoft will offer an upgrade for existing Liberty users
* Note that we plan to re-release our “Intervention CCR” (iCCR) in 2021. The unit was withheld due risk of loop being force dived when unsafe (pending re-release 2021).This enables the diver the option to manually trigger bailout to a known safe OC gas at any time with one finger and/or auto-bailout the diver if loop gas being breathed reaches unsafe level. Either Hi/Lo PPO2 or high End-Tidal CO2.
**For CE certification the recommended Apocalypse Type IV CCR scrubber duration is 2hr 45min to a maximum dive profile surface to surface of 100m in 4’C water to 2.0% SEV (20mb) at the mouth.
***iCCR (2009) 3x digital galvanic coax, iCCR (2021) x2 galvanic 1x solid state
****All performance data near near identical to single scrubber option other than increased scrubber duration of up to 5 hrs to 100 m profile in 4’C water)
Published Testing: .pdf
* CisLunar series, MKVI 2009, SE7EN 2013, SE7EN+ 2019
** 40 m coldwater EN14143
*** Backmounted Trimix 10/70, 40M test: Backmounted Air
**** SE7EN+ Sport EU incl (harness, wing, computer, cylinders and sensors)
  • Halcyon Sidemount

Note – Vobster Marine Systems were acquired by UK-based NAMMU Tech, which plans to rename and re-issue a version of the VMS Redbare (formerly the Sentinel) at some point in the future. See: Atlas CCR


Rey says he’s sticking to open circuit. What’s a Santa to do?

Sidemount Rebreathers

*Pre 2021 units are upgradebale
* For a tour of KISS rebreathers see:

Frontmount Rebreathers

*Tested with standard DSV, 6l OTS counterlungs, Upright/face forward, 40 m depth, 40.0 lpm RMV, Air diluent
**Tested with standard DSV, 45° head up/feet down orientation, 40 m depth, 40.0 lpm RMV, Air diluent
*** Micropore ExtendAir Cartridge:
180 liters of CO2 @ < 50 deg F [<10 C] (130 minutes @1.35lpm CO2)
240 liters of CO2 @ 50-70 deg F [10-20C] (180 minutes @ 1.35lpm CO2)
300 liters of CO2 @ >70 deg F [>20C] (220 minutes @ 1.35lpm CO2)
Test Parameters: 40 lpm RMV 1.35 lpm CO2130 fsw (40 m) depth Granular duration may be similar, but can vary greatly depending upon the type of granular and packing technique

 Download our two master spreadsheets, one for back mounted units and one for sidemount to compare rebreathers.

Special thanks to Amy LaSalle at GUE HQ for her help assembling the feature spreadsheets.

Michael Menduno is InDepth’s editor-in-chief and an award-winning reporter and technologist who has written about diving and diving technology for 30 years. He coined the term “technical diving.” His magazine aquaCORPS: The Journal for Technical Diving (1990-1996), helped usher tech diving into mainstream sports diving. He also produced the first Tek, EUROTek, and ASIATek conferences, and organized Rebreather Forums 1.0 and 2.0. Michael received the OZTEKMedia Excellence Award in 2011, the EUROTek Lifetime Achievement Award in 2012, and the TEKDive USA Media Award in 2018. In addition to his responsibilities at InDepth, Menduno is a contributing editor for DAN Europe’s Alert Diver magazine and X-Ray Magazine, a staff writer for, and is on the board of the Historical Diving Society (USA)

Amanda White is the managing editor for InDepth. Her main passion in life is protecting the environment. Whether that means working to minimize her own footprint or working on a broader scale to protect wildlife, the oceans, and other bodies of water. She received her GUE Recreational Level 1 certificate in November 2016 and is ecstatic to begin her scuba diving journey. Amanda was a volunteer for Project Baseline for over a year as the communications lead during Baseline Explorer missions. Now she manages communication between Project Baseline and the public and works as the content and marketing manager for GUE. Amanda holds a Bachelor’s degree in Journalism, with an emphasis in Strategic Communications from the University of Nevada, Reno.

Kenzie Potter Stephens is a production artist for InDepth as well as part of the GUE marketing team. She earned her BS degree in Industrial Engineering and Marketing at the Karlsruhe Institute of Technology (KIT) in Germany, which assists her in using her multicultural upbringing to foster international growth within the community. In addition to her activities as a yoga teacher and an underwater rugby trainer, she has completed her GUE Tech 1 and Cave 1 training and is on her way to becoming a GUE instructor. Not letting any grass grow under her feet, she has also taken on a second major in biochemistry in order to create a deeper understanding of our planet’s unique ecosystems as well as the effect of diving on human physiology.

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