Glen Fruin's Little Secret

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DURING the Second World War the battle against the German Navy was key to defending British supply routes.

Not least of our problems was launching bombs, depth charges and torpedoes without them breaking up or setting off their fuses prematurely on impact with the sea.

A particular problem for air launched projectiles was the tendency on entering the water to veer off in anything but the right direction which, without any active guidance system, greatly reduced their effectiveness.

Two experimental facilities were set up in the early 1940s, one by the Admiralty at Coulport to test water entry of torpedoes and a second by the Ministry of Supply in Glen Fruin to deal with air dropped munitions and to explore solutions for amphibious aircraft landing on water.

AHBRE-Norman-1Coulport was operated as an outstation of TEE (Torpedo Experimental Establishment) Gourock and launched full scale torpedoes into Loch Long. It also hosted a mortar for air launching mines into a recovery net on a cableway across the loch and test cells for propulsion systems using HTP (High Test Peroxide) a particularly unpleasant and explosive fuel.

Glen Fruin was the hidden asset that supported the work of the Marine Aircraft Experimental Establishment at Rhu. Apart from a launcher very similar to the one at Coulport it also boasted an enormous water tank, one wall of which consisted of glazed panels to facilitate observation of the projectiles passing through the water surface.

As it was tucked away at the head of the Glen very few knew it existed and even fewer knew what it was for.

AHBRE-Norman-3Measurements in the 1940s were pretty well confined to the use of high speed photography and with the water entry phase lasting around two tenths of a second there was not much time for taking snaps.

Since the early programmes were geared to finding ad hoc solutions to problems from the front line such limitations were acceptable, but after the war a more considered approach was necessary.

In 1950 it was decided to bring many of the disparate experimental facilities under unified managements and develop coherent research programmes. Coulport, Glen Fruin and the range at Loch Goil were amalgamated into the Admiralty Hydro-Ballistic Research Establishment — AHBRE.

The brief was, at the time, rather wittily summarised as “. . . reduce the steady growth of our underwater ballistic ignorance.”

My father, James Norman, who had been instrumental in setting up the range at Loch Goil during the war, volunteered to move to Scotland from the new parent site at Teddington — the Admiralty Research Laboratory.

AHBRE-Norman-4Highly organised and a practical engineer with an enquiring mind, he set about devising a programme and took advantage of the rapid growth of electronic technologies to build a unique and productive research facility.

New launcher designs based on the catapults used to launch aircraft at sea and others using rubber bands allowed rapid turn round and repeatable results. They were capable of delivering models at speeds in excess of 300mph.

Maintenance of the tank had not been a high priority during the war and there was an increasing tendency for windows to crack and blow out as the rusty frames expanded, let alone when a projectile veered sideways.

Always spectacular, a square jet of water would blast against the opposite wall, but the delays for repairs and the filtering of the very peaty Fruin water to achieve the high optical clarity required for high speed photography were very inhibiting.

A regime of annual drain downs, repairs and painting greatly reduced the problem and a regular order for Bostic sealant prevented the water getting into the space between the frame and the glass. The glass wall was 140ft long and 45ft high with 466 armoured glass panes some 1¼ inches thick. so Bostic was often in short supply in West Dunbartonshire.

AHBRE-Norman-5Newly developed accelerometers were bought from the United States — a very long winded process — and, with ever better photographic equipment, transformed the understanding of the enormousforces involved when hitting the water at 100+ mph.

Lateral accelerations of 180g were typical on entry so the reasons for deviation from the intended course were soon obvious. Not surprisingly the shape of the head of the torpedo was also crucial.

What was surprising was that an almost totally flat head with slightly rounded corners proved optimal — it also proved ideal for housing the increasingly capable sonar sensors that fed the ever more versatile guidance systems.

While testing at smaller scales at Glen Fruin was quicker, cheaper and more convenient, the results initially bore little comparison with full scale results from Coulport. This proved to be because the viscosity (stickiness) of the water and the pressures in the gas cavities generated on entry were not scaled properly.

Many fixes were tried including commandeering most of the local stocks of Alka Seltzer to alter the characteristics of the water surface. In the end a thin layer of very hot water was found to work perfectly.

AHBREʼs mixed parentage often produced administrative anomalies. The stores at Coulport were run under Naval Stores rules while those at Glen Fruin used Ministry of Supply rules. Both now belonging to the Admiralty, the routine stores audits were always
passed at Coulport but failed at Glen Fruin.

AHBRE-Norman-6In 1956 the first of many rationalisations took place with The Way Ahead report. Jim Callaghan, the then Chancellor, sought savings — nothingʼs changed! — and Coulport was put under Care and Maintenance.

Maintaining a steel structure in a corrosive atmosphere beside a sea loch without spending any money demonstrated that Whitehall has always been a little disconnected from reality. It was eventually dismantled before it fell down.

However the impending closure was going to curtail the amount of full scale results available so the strike rate of firings was increased to one and even two per day.

Since no written instruction to close had been received at Coulport, my father acted as a true civil servant and carried on regardless until at last he received a peremptory order to cease operations!

But he had succeeded in accumulating a large body of data that was fundamental to solving the scaling problems shown up at Glen Fruin — it also kept the analysis team busy for quite a while. Later the Coulport site was to be developed as the RN Armament Depot for Trident.

AHBRE-Norman-7Apart from a long series of systematic water entry tests, full scale at Coulport and at smaller scales at Glen Fruin, the tank proved invaluable for other explorations.

Perhaps the most interesting was the development of techniques to allow crew to escape from aircraft that crashed in the sea. Unless the pilot was very quick to release the cockpit cover, the build up of water pressure made this impossible.

In collaboration with the Institute of Naval Medicine and Martin Baker (of ejection seat fame), Glen Fruin devised techniques that ensured that pilots who survived the initial ditching only had to fire their ejection seat in the usual way in order to rise rapidly to the surface.

Even the US and French navies took part — the French team proving to be extremely efficient with their Etendard aircraft, we are told.

The RN surgeon/ diver who made the first ejections underwater went on to become Surgeon Rear Admiral Rawlings, the top doctor in the Navy. I think he
earned it. A full size Sea Lynx helicopter was also dunked to demonstrate its ditching routines.


The original team at Coulport, Glen Fruin and Loch Goil in 1951.

In an interesting twist of fate the late 1960s saw a requirement for a launcher again to test full size torpedoes and weapon systems. My father was commissioned to deliver the requirement and a mobile floating launcher was built at the Ailsa Shipyard in Troon with the launcher design provided by Brown Brothers.

My father finally retired in 1969. Glen Fruin continued under the direction first of Jackie Littlefair, then Alasdair MacPherson — a native of Cove, son of the local policeman — and Ian MacDonald who was one of the original crew back in 1950.

Requirements for such facilities declined as sophisticated instrumentation, microprocessors and computers became commonplace and full scale trials became routine.

However the body of hydro-ballistic knowledge established at Coulport and Glen Fruin continues to provide sound validation for the complex mathematical models that are used today to predict the trajectories of projectiles passing through the surface of the sea.

In the 1980s the site was steadily run down and is now part of the Army training facilities in the area. The tank itself is now Category B listed by Argyll & Bute Council for Historic Scotland (Ref: HB51003, Item 84), but without considerable investment is unlikely ever to be used again for its original purpose.


The Glen Fruin team about 1969.

© David Norman 2010.