LR5 and Submarine Rescue
The loss of the USS Thresher in 1963 and Scorpion in 1968 lead to the formation of the Deep Submergence Unit in San Diego and DSRV’s (Deep Submergence Rescue Vehicles) Mystic and Avalon in 1970. These are delivered by specially modified US, French and British nuclear submarines. Their 1,500m depth capability exceeded that required of a functional rescue submarine by a considerable margin but the story is that this had more to do with cold war exploits than expected future developments in US submarine hulls. The UK was entirely dependent on the US for submarine rescue until 1988 when the LR5 became the UK’s first dedicated rescue submersible.
Originally the LR5 was a diver lock-out submersible built by Slingsby and operated by British Oceanics. Slingsby of Kirkbymoorside in Yorkshire built sailplanes, first of traditional materials and then in GRP, the new super-material. They pioneered the use of the advanced techniques that are commonplace today and became very good at it. An offshoot of the shipbuilder Vickers in Barrow-in-Furness, Vickers Oceanics, recognised the potential of composites in submersible construction and so Slingsby was purchased to gain access to their unique expertise and technology. Slingsby were then commissioned to build a series of GRP hulled submersibles to work in the oil sector, mainly the North Sea. The second last of these was LR5 built in 1978 that operated down to 457 metres. It had a GRP command module, propulsion module and battery pods. The lockout chamber was made in steel by Perry in West Palm Beach and in this regard had many similarities to PC-18 boats. A final model variant, (LR5K) was built in the 90’s for the South Korean Navy as a rescue submersible. LR1 was actually the Perry PC-15 but named after Vickers’ master ship builder Sir Leonard Redshaw. LR2 had limited use as did LR3 which ended up in the Royal Navy Submarine Museum in Gosport. LR4 never dived and was used for spares before LR5 was fully modified.
Following Roger Chapman’s close shave in Pisces III in the Atlantic British Oceanics started developing submarine rescue systems for the Royal Navy, undertaking initial trials with L1 (PC15) and then supporting the conversion of LR5 into a rescue submersible. This required the addition of a larger diameter hemispherical section – the ‘skirt’ under the lockout hatch to mate and seal with the rescue hatch now fitted to the majority of the world’s naval submarines. LR5 proved very successful as a surface-ship launched rapid-reaction, flexible rescue vehicle for the UK and Northern Europe; the addition of a portable ‘A’ frame meant the system could be air transported and deployed from a ‘ship of opportunity’. Until 2008 LR5 formed the basis of the UK Submarine Rescue Service until the arrival of the new Perry-Slingsby NSRS. Today LR5 is operated by James Fisher for the Australian Navy from Perth.
As a rescue submersible, LR5 had two main shortcomings: first it could only really rescue 5 people at a time and if they had been under pressure (a likely scenario), they could not be transferred easily to a decompression chamber. In 1997 a study was conducted by RUMIC, (later JFD), to look at the feasibility of increasing the rescue compartment capacity to 16 and adding a Transfer under Pressure (TUP) facility, now standard on all submarine rescue vehicles. I was very fortunate to be involved in the design work of this upgrade programme from the outset.
The aft propulsion module and the diver lockout chamber were replaced with a single new rescue chamber compartment made of Q1N (HY80) just 13mm thick. It was a challenge to equal the structural efficiency of GRP even with advanced steels. The main motor was removed and propulsion provided by external pod-mounted motors and thrusters and the rear of the rescue chamber was fitted with a large transfer under pressure (TUP) hatch and clamp ring to attach to a deck mounted decompression system.
The final conversion in 1999 took LR5 out of service for just 6 weeks after which it was re-commissioned as a fully TUP-capable rescue submersible. This has proved very effective and has become the baseline design pattern for all submarine rescue vehicles from that point on. Under pressure from Lloyds, and because the NSRS program was delayed by 5 years, a further major refit upgrade was completed in 2005, with the GRP Command module and battery pods replaced by Q1N, which is easier to assess from the modern QA perspective. This has been a structural challenge all the way through and now there are precious few pieces of LR5 remaining apart from the name and possibly the pilot’s seat.
The NSRS, in service since 2008 and fully air portable with its own TUP facility and decompression chambers provides global cover. A similar vehicle built by Perry Slingsby for the Chinese (LR7) at the same time, plus DSAR 5 for Korea and DSAR 6 for Singapore, both by James Fisher, are all built to the same basic pattern. The US replacement for the DSRVs – the Submarine Rescue Diving and Recompression System (SRDRS) also adopts the stern transfer lock although the actual submersible is a single compartment, tethered vehicle.
The future of composites for submarine hulls remains open. Whilst the various forms of composites have long been accepted into almost all other product areas from aircraft to boats, from F1 cars to artificial limbs the ultra-conservative (submarine) submersible classification societies are unwilling to consider a material that is subject to so many uncontrolled variables during its construction. For vehicles that do not require approval by the big three, ABS, Lloyds or GL, composites do have a great future. Despite my present trading name, Steel Fish Ltd, my next boat will be composite.
