Appendix 1 UK Military Hovercraft Trials Units Background When Christopher Cockerell was seeking support for the development of the hovercraft principle, it was the intervention of the late Earl Mountbatten that was of signifi cant help. With his background in Amphibious Warfare, he immediately saw the potential for this new concept, so much so that it was initially classifi ed as Top Secret. Eventually, the Saunders Roe, SR.N1, was built and launched on 11 June 1959 to further evaluate the potential of the concept. This new vehicle attracted great pub- licity and interest in the UK. Military interest led to the formation of an Interservice Hovercraft Working Party in 1961 and the formation of the Interservice Hovercraft (Trials) Unit (IHTU) at HMS Ariel (later HMS Daedalus), at Lee-on-the-Solent just west of Portsmouth harbour. IHTU personnel were drawn from the Royal Navy, Royal Marines, Royal Air Force and the Army. The different Service backgrounds and training assisted both in routine maintenance and fault fi nding on these special craft. Additionally, after the traditional 3-year tour, personnel were drafted to active units and able to spread the message about the usefulness of amphibious hovercraft. Figure A1.1 shows the Unit in the NHTU days with SR.N6, BH 7 and VT 2 craft present. The Early Days In order to evaluate hovercraft military potential, to start with craft were hired from their manufacturers and operated from Lee-on-the-Solent. These evaluations served the double purpose of enabling Service personnel to gain experience of hovercraft operations and assisting manufacturers in the development of their craft. L. Yun and A. Bliault, High Performance Marine Vessels, 323 DOI 10.1007/978-1-4614-0869-7, © Springer Science+Business Media, LLC 2012 324 Appendix 1: UK Military Hovercraft Trials Units Fig. A1.1 HMS Daedalus—Base for Naval Hovercraft Trials Unit The fi rst major evaluation was conducted with the SR.N1, at the time fi tted with 18 in. skirts. Trials comprised many circuits of an overland hover way, which included steps and waves constructed out of shingle. In a second series of trials, this time with 4 ft 6 in. depth skirts fi tted, the craft was operated over saltings with gul- lies nearly 3 ft deep and between 4 and 15 ft wide. SR.N1 was an experimental design, but SR.N2 was a practical craft and military trials included a passage from Cowes to Portland in seas up to 6 ft from crest to trough and a circumnavigation of the Isle of Wight in calm conditions, at an average speed of 58 knots. IHTU were also involved in demonstrations of SR.N2 in Montreal, operating on the St. Lawrence River and the Lachine Rapids. Vickers Armstrong also produced early hovercraft and the VA 1 was based at Lee-on-the-Solent, carrying out obstacle clearing trials over straw bales on the airfi eld. The larger VA 2 was taken to RAF El Adam, in North Africa to conduct trials in desert conditions. The fi rst ever comprehensive overland trials with a hovercraft saw VA 2 complete journeys totalling nearly 200 miles at speeds up to 38 knots. Skirt wear over the sand was severe, but neither dust, nor the terrain were problems. It became obvious from the evaluations of hovercraft hired from their manufac- turers that in order to fully evaluate hovercraft military potential, craft owned by the Unit would be needed. To this end, delivery was taken of the SR.N3 and three SR.N5s from the British Hovercraft Corporation in July and September 1964, respectively. Appendix 1: UK Military Hovercraft Trials Units 325 Fig. A1.2 SR.N5 in Sumatra Jungle The Interservice Hovercraft Unit (Far East) Two of the SR.N5s—XT 492 and XT 493—were military versions, modifi ed for operations in the tropics, to be used by IHU(FE). After a period of training in the UK, the Unit moved to Singapore, at the end of 1964, for a 2-month work-up period (Fig. A1.2 ) . The Unit deployed to Tawau, Sabah, to assess the value of hovercraft as a general military load carrier in the type of terrain encountered in the area (Fig. A1.3 ). Logistic support was normally carried out by road vehicles, civilian river craft, heli- copters or assault boats. Road communications in the area were extremely limited, river craft were hampered by the profusion of fl oating debris and by shallow water at low tide, and the use of helicopters was strictly limited, in order to conserve hours for more important tasks. However, at Tawau, the craft covered nearly 6,400 nauti- cal miles and carried 1,600 passengers and 110 tonnes of freight. The craft were moved to Thailand, where their amphibious capabilities were demonstrated, both in calm conditions and winds up to 40 knots, seas up to 7 and 5 ft surf. The craft were driven up and down river rapids fl owing at speeds in excess of 12 knots, with rocky outcrops and through gaps not much wider than the craft. Tight turns in the rivers were often negotiated by using the infl ated skirt as a fender against the river banks. 326 Appendix 1: UK Military Hovercraft Trials Units Fig. A1.3 SR.N5 at sea Fig. A1.4 SR.N6 in Falklands In Sarawak, a journey of over 300 miles along the Rayong River was completed. The fi rst 110 miles were over open river, but from then onwards, commencing with the Pelagus Rapids, the route became increasingly diffi cult. The journey normally takes 8–12 days by long boat—the hovercraft completed the journey in less than 8 h. Appendix 1: UK Military Hovercraft Trials Units 327 It should be remarked here that the Far East Unit was successfully maintaining gas turbine-driven craft with aerospace structures and early generation skirts to operate in high humidity equatorial environment, making journeys into extreme remote locations. Such performance did not go unnoticed in the Navy or Royal Marines, and craft were sent on trials or demonstration deployments to many challenging locations worldwide in the late 1960s and early 1970s, including detachment of a Navy SR.N6 to the Falkland Islands for a summer season tour in late 1967 (Fig. A1.4 ) Trials and Evaluations The SR.N3—the World’s fi rst military hovercraft—undertook a series of role evalu- ations, including operating as an RAF marine craft, anti-submarine warfare (ASW) trials for the Royal Navy and operations in the logistic role for the Army. The craft also featured in the fi rst shop window for hovercraft—Hover show 66. The SR.N3 and later the BH 7 featured in trips abroad, but as with early commercial hovercraft ferries, the smaller SR.N5 and SR.N6s proved to be the “work horses” of the Unit. SR.N5 XT 657 was fi tted with a comprehensive instrumentation package to record trials data during performance trials, conducted by Royal Aircraft Establishment, Bedford and Admiralty Experiment Works, Haslar personnel. Bedford trials included static tests to measure propeller thrust, control forces and pitch and roll stability, lift system effi ciency, hover height and daylight clearance. Sea trials included performance measurements to enable the variation of drag com- ponents with forward speed to be obtained, control effect investigations and seakeep- ing trials at three different weights and in a number of environmental conditions. On return from the Far East, XT 493 was refurbished, and after employment on training and general logistic tasks, was prepared for surf trials. These were con- ducted at Saunton Sands on the North Devon coast, also involving an SR.N6 Mk 2. It was found that the best method to approach the beach was to position the craft between surf crests and adjust speed, until the craft and surf approached the shore at the same speed. Leaving the beach proved to be best on a track at 45° to the surf. A military version of the SR.N6 conducted naval trials at Portland, investigating use as an anti-Fast Patrol Boat training craft, a helicopter safety boat and various exercises with ships working up with Flag Offi cer Sea Training. A major trial involved investigation into the best geometry for an overland “hover way” con- ducted at Longmoor, Hampshire, culminating in the construction of a 0.83 mile long hover way, with curves, ascents and descents, completed by the craft at the target mean block speed of 25 knots. British Hovercraft Corporation, BH 7 The larger BH 7 completed a very comprehensive series of acceptance trials, oper- ated by a joint team from IHTU and the British Hovercraft Corporation. Once accepted into service, crews were worked up to operate and maintain the craft. 328 Appendix 1: UK Military Hovercraft Trials Units Cold weather trials were conducted during March and April 1972, in Sweden and the Gulf of Bothnia. The journey of some 1,600 nautical miles to Sweden and on to Ranea, the northernmost navigable point of the Gulf of Bothnia, was one of the longest journeys undertaken by hovercraft operating under its own power. Operating so far from base, in relatively harsh conditions and over surfaces not previously encountered, presented the craft and crew with a major challenge. This challenge was met and the trials successfully completed. The results attracted sig- nifi cant interest, particularly the demonstrating of ice breaking by hovercraft. Evaluation of long-term habitability and reliability was tested when the BH 7 was used on Channel Patrol, operating from Pegwell Bay, Kent. The craft was directed by HM Coastguards at St.