John Alfred Jennison (1898-1950)
The inventor of the 'pop-top' caravan
My thanks to Jeff Gill (the grandson of John Jennison), Richard Dickins (Australian RV historian) and Vintage Caravan Forum members 'Aussieute' and 'Cobber' for their assistance with photos and information for this article.
How do you create headroom inside a caravan while keeping it aerodynamically efficient under tow? Australian engineer John Jennison found an elegant solution to this problem in the 1930s and in doing so created one of Australia's most popular types of caravans today - the 'pop top'.
Salisbury Service Station
Born in Sydney in 1898 and orphaned at 14, John Jennison wanted to be an engineer from an early age. He worked at a number of automotive coachbuilders and engineers in Melbourne and Adelaide including Holden Motor Body Builders Limited. Spotting a garage for sale in Salisbury, South Australia on the return leg of a motorcycle trip from Adelaide to Perth in 1926, Jennison jumped at the opportunity to put his newfound engineering skills into practice. As the proprietor of the Salisbury Service Station he experimented with the construction of various vehicles including a racing car and a speed boat (see below).
On a hot night in Salisbury in 1933 his wife Doris was leafing through an English caravan magazine (The Caravan magazine was first published in that year) and expressed interest in taking a holiday in a caravan. Jennison immediately picked up pen and paper and the two sat together until the early hours of the morning designing their first caravan. By the next morning it was under construction.
Jennison's First Caravan
With no other template to follow, Jennison’s first caravan was designed along English lines. It was full height, had a curved roof sloping down at front and rear and had limited ventilation. It would have been heavy, hot and stuffy in a South Australian summer. It was finished just before Christmas 1933 and created much local interest. After taking it on a somewhat stressful summer holiday due to the need to keep a watchful eye on the stability of the new caravan, Jennison sold it and built a second one with a few improvements.
When Sydney businessman Bertram Hassell came to inspect the second caravan with a view to buying it, he felt that it was too tall to tow safely behind a standard car. But Hassell had enough faith in Jennison's construction quality to commission the building of a reduced-height caravan. Jennison wondered how he could lower the roof of the caravan under tow while still creating enough headroom when the caravan was parked.
The Birth of The Pop-Top
British caravan designers had struggled with caravan aerodynamics during the 1920s. The solution of some British caravan makers such as Eccles and Shadow was to build 'collapsible' caravans, where the entire roof and top half of the caravan dropped like a chocolate box lid over the lower half prior to towing. The solution appeared elegant but in practice required complex lifting mechanisms that would often fail due to road vibrations and weather seals that would leak in the rain. German caravan maker Arist Dethleffs built caravans with elevating roofs in the early 1930s but these had to be raised and lowered manually.
In Australia the low-height camper trailer was a simpler solution for early makers – it was better suited to local weather but still meant handling canvas.
Jennison's solution to the aerodynamic limitations of the full height caravan was to raise the roof only. When the roof was lowered before travel the caravan was more aerodynamic, but when raised at camp it still provided both headroom and ventilation. To raise and lower the roof Jennison used an ingenious method of linking four 'worm-drive' rods at each corner of the caravan to a continuous chain, requiring only a single handle to operate the roof. When the roof was raised, Jennison proposed a detachable skirt of canvas to be attached between roof and caravan to make it waterproof.
Jennison patented his idea in 1935. The idea was called a 'movable roof' in the patent but was later named by Jennison a 'telescopic roof mechanism'. Later Australian caravanners came to call such a design the ‘pop-top’.
Jennison's patent is available to download below:
Photos taken at the rear of the Salisbury Service Station in the mid 1930s show the structural lightness of Jennison’s first caravan frames. But they also show how Jennison struggled with the rigidity of his early pop-top prototypes. A hand-drawn cross-member on the photo below shows where Jennison felt it was necessary to increase the lateral strength of the frame – on the back of the photo is written, “suggested tie-rod position shown in snap removable when camping”. Some later Jennison pop-top roof models show a permanent cross-member in the roof to address this problem. A rare Jennison pop-top prototype from about 1934 (recently restored by Vintage Caravan Forum member Aussieute) used Masonite panels instead of roof skirts. It appears these were used in early production models but may have been replaced by canvas in later models.
The Jennison Road Cruiser
In 1935 the new type of caravan was delivered by ship to Bertram Hassell in Sydney. It was met with sufficient enthusiasm by its new owner for a second one to be ordered. This time the Jennisons decided to deliver the caravan personally and make a permanent move to Sydney to start up a business building this new type of caravan. It was to be called the Jennison Road Cruiser. Jennison registered his new business under the name of Jennison Road Cruisers on 15 January 1936. Hassell helped Jennison find suitable business premises in Cremorne, North Sydney.
In the mid 1930s caravanning was still in its infancy in Australia. The Great Depression was having a severe impact on jobs and family budgets, so cars and holidays were luxuries. The best way to sell caravans was to hire them out to potential buyers for short periods so they could become acquainted with the caravan lifestyle without major capital expenditure. In 1936 Jennison built a small fleet of Road Cruisers incorporating his patented telescopic roof. These were made available for hire and were soon in demand.
As his confidence grew and hires turned slowly into sales, Jennison introduced a new duck-tailed Streamlined Road Cruiser in late 1936. In early 1937 Jennison had enough orders to warrant moving to a larger factory on Military Road, Cremorne. On 24th April 1937 he changed the name of his company to Jennison Caravan Cruisers. In May 1937 the duck-tailed model was renamed the Supreme Jennison Caravan Cruiser.
Jennison worked with a number of different people from the time he formed his fruitful association with Hassell in 1934 or 1935 until his death. They included investors, buyers and business associates or partners. Jennison seems to have had a particular skill in building business relationships.
A beautiful selection of photos taken by Australian artist WEP Pidgeon on a tour of the Wyalong Valley in New South Wales in his Supreme Jennison Caravan Cruiser in 1937 can be found here.
The Demise of the Pop-Top
By the late 1930s larger caravans had become popular thanks to an improving economy, more powerful automobiles and diminishing concerns (albeit among salesmen rather than engineers) about the impact of aerodynamics on towing stability and fuel consumption. The small caravan fell out of favour.
So in order to meet market demand, in late 1937 Jennison branched out into the design of a larger caravan, also called the Supreme Jennison Caravan Cruiser, that didn’t have a pop-top roof. Such a roof would always be more complex and more expensive to build than a flat roof, and in any event may have compromised the structural integrity of a larger caravan.
Jennison still managed to achieve a streamlined design with adequate head height in this caravan by introducing a lantern roof (a partially raised section of the roof incorporating thin, side-facing windows) and the drop axle carried over from the Road Cruiser, allowing a lower floor. Advertising suggested that this caravan incorporated the “latest English and American designing”, so Jennison was clearly watching overseas developments closely.
It’s not clear how long production of the telescopic roof caravan continued, but it was no longer being actively advertised in 1938. Meanwhile, by that year the hire side of Jennison’s business was booming. According to Jennison Managing Director S.V. Bligh in June 1938:
"This company, since last Easter, has found it necessary to treble its hire fleet - all of the larger type - and could still utilise many more.”
The hire of big caravans was now big business.
Jennison and the Transport Engineering Co.
Between 1938 and 1940 Jennison collaborated with another Sydney company, the Transport Engineering Co. which produced Nomad caravans. Of this collaboration Jennison’s wife Doris later wrote:
"Some time later J.A.J (Jennison) joined the staff of Nomad T.E.C. as designing engineer, taking with him a new design. This was a streamlined domed roof coach. It was a really beautiful job, but its construction was too costly to be able to produce it profitably for sale in those prewar days, before caravans became a must with so many of the motoring public. Modification was the only answer to this, and the J model Nomads that followed, formed a very fine hire fleet which was always popular and kept very busy."
New research by Australian RV historian Richard Dickins suggests that the collaboration between Jennison and Transport Engineering Co. owner Henry Young was a particularly fruitful one for both of them. With Jennison’s input Transport Engineering Co. developed new caravans under their ‘Nomad' brand (including a Model ‘J’, possibly for Jennison), whilst Jennison was able to test some new caravan design ideas of his own. Many of the ideas and designs resulting from this relationship were built into Jennison’s first post-war and possibly finest model, the Jennison Pathfinder. Further important information and photos relating to this partnership are likely to emerge from Dickins' research.
The Wildeshott Caravan
During 1938 Jennison also produced a ‘toaster-shaped' caravan on behalf of clients Mr. and Mrs. Cole, who called their caravan Wildeshott and which Jennison badged under the name 'Jennison Coach'. The Wildeshott caravan was similar in size and shape to the smaller trailers of the US company Covered Wagon, but it’s not yet clear whether Jennison built this caravan alone or with external help.
In 1939 just before the war, Jennison found time to introduce one more model under the ‘Road Cruiser’ brand that was not dissimilar to some Nomad models.
The Aristocrat of Caravans
In 1946 Jennison’s pre-war relationship with Transport Engineering Co. produced an unexpected bonus. Transport Engineering Co had ceased production in 1942 as a response to the war effort. Along with the rest of the country, the company was facing post-war shortages of fuel and materials, so owner Henry Young decided not to restart his trailer engineering business in Sydney and transferred the entire business to Jennison, possibly as a gift. Following the transfer, Jennison changed the name of his company to the Jennison Trailer Engineering Co. in April 1946. Owning this company gave Jennison the opportunity and the means to focus on the caravan for which he is best known, the Jennison Pathfinder.
The Jennison Pathfinder was introduced in September 1946. Marketed initially as 'Australia’s Finest Caravan' and 'The Caravan of Distinction', Jennison finally settled on ’The Aristocrat of Caravans’. As with his previous caravans, in order to reinforce the engineering credentials of his products Jennison noted in advertising material that the Pathfinder was 'Tested by the NRMA’ (the National Roads and Motorists' Association). He also claimed that his caravans were 'Built by Trailer Engineers since 1930', although there is currently no record of Jennison caravans that far back.
The Pathfinder represented everything that Jennison had learned about caravans up to that point. It was streamlined, superbly finished and attention to detail showed everywhere. Initially four models were produced (10, 12, 14 and 16ft), all with a large ventilating roof. Other features included hydraulic jockey wheel, cranked axle, vacuum servo-brakes, double-panelled walls, electric wiring for 6 and 240 volts, a 3-burner stove, a water pressure system, an ice chest and a bath. Internal cabinetry was of the highest standard and storage was plentiful.
By 1948 other features had been added including an internal shower and a wall-mounted radio. As prices and availability of aluminium improved after WW2, a prototype aluminium Pathfinder was built in 1949 and became a permanent feature in 1953. Aluminium window frames were incorporated at the same time. Jennison was amongst the first Australian caravan manufacturers to use aluminium cladding and window frames.
Below are some publicity photos of the Jennison Pathfinder taken in 1948 (supplied by grandson Jeff Gill):
Pathfinders were widely praised by owners for their quality. They were for example the caravan of choice for the Travelling Showman’s Guild, whose owners kept the company busy at Easter with annual caravan services whilst they attended the Royal Easter Show in Sydney. Reviews in the press were uniformly positive.
Jennison’s Final Years
Prior to his premature death in 1950, Jennison remained busy with Pathfinder production and modification. Befitting a man who found 48 hours in each day, he also continued other projects. He modified US-made Willy’s Jeeps into four-wheel drive wagons, allowing them to be used in remote areas in conjunction with his caravans. He also petitioned his local council (North Sydney) to provide powered caravan sites on council camping sites. As a family man, Jennison even found time to make toy models of the Jennison Pathfinder for children.
Jennison died in Sydney on 19 October 1950.
Post-1950 Jennison Caravans
After Jennison's death the Jennison Caravan business was sold to Richard Pym and production was moved to Artarmon in North Sydney. The new owners continued to produce caravans under the 'Jennison Pathfinder' brand until 1961, after which production paused twice with the name ‘Jennison' being dropped partially in 1962 and completely in 1964. By 1969 both the 'Jennison’ and ‘Pathfinder’ names had disappeared from newly manufactured caravans.
A company advert in the Sydney Morning Herald of 20 April 1963 stated that a Jennison Pathfinder was chosen by Donald Campbell for his personal caravan as part of his land speed record attempt with The Bluebird on Lake Eyre in 1963. This has not been verified.
With strong market competition and the absence of Jennison at the helm, Jennison caravans built in the late 1950s into the 1960s were no longer seen as ‘The Aristocrat of Caravans’, and by the late 1960s the Pathfinder had sadly lost its way.
Jennison's Other Vehicles
Although building caravans was Jennison's passion, he built other vehicles too. These included:
Top left: A racing car built in the late 1920s
Top right: A speedboat built shortly after the racing car
Bottom left: A 'Car of the Future' built on an Austin 7 chassis with a wooden frame and bondwood bodywork in the late 1930s
Bottom right: A stretched Willy's Jeep designed to tow Jennison's caravans off-road more-easily (late 1940s)
All of these projects were hobbies carried out in Jennison’s back yard or factory with limited resources and even less time. They show a remarkable breadth of engineering talent as well as a sense of fun and adventure (all photos courtesy Jeff Gill).
Conclusion
John Alfred Jennison was a talented and influential Australian caravan designer and builder. Making vehicles of all kinds was his passion, and solving engineering problems was his forte. The pop-top caravan roof was his main technical achievement, but he was also an innovative caravan designer. Cranked axles, lowered floors, lantern roofs, hatches, smooth corners and streamlined contours were not new, but Jennison combined them in a way that had not been seen before in Australia and to a standard that would set a benchmark for decades to come.
As a multi-disciplined engineer in the field of early RVs his achievements mirror those of Glenn H. Curtiss of the USA and Charles Louvet of France.
Australian caravan owners of today, those with pop-tops above all, owe him a debt of gratitude.
A Jennison Pathfinder kennel and toy trailer (courtesy Jeff Gill)
Andrew Woodmansey
July 2022