In 1919, Great Britain presented each of its Dominions with an “Imperial Gift” of about 100 aircraft and a mass of associated equipment—leftovers from World War I. The U.S. Navy added a dozen Curtiss HS2L flying boats, no longer needed to patrol for U-Boats lurking in the approaches to East Coast ports. The Canadian Government, apprehensive of operating and maintenance costs, very reluctantly accepted this gift package. They were, however, the means of building Canada as we know it today.

Little of Canada was mapped in 1919. Sections in the south and along the traveled waterways had been surveyed, but vast expanses remained of “unknown country.” Maps were urgently needed by a rapidly growing nation to establish provincial and national borders; identify and exploit a vast range of natural resources; build hydroelectric power stations and transmission lines, highways, canals, and railways; settle immigrants; drain and irrigate land; and plan towns and cities.

Canadian pilots—those who survived the folly of Flanders—put the “white elephant” gifts to work. Over the next two decades, they photographed much of Canada from the air, and engineers developed techniques to produce accurate topographical maps. It all started at Rockcliffe. In those days, flying boats and float-equipped aircraft were all that could fly any distance over Canada simply because there were few airfields. Sheltered spots on rivers and lakes became “air harbours.” The only base for both water- and land-borne aircraft was at Rockcliffe, where the Ottawa River was used by flying boats.

Alongside, a grass airfield was built on Department of Militia and Defence land, unwanted by anyone else because it lay in the danger area behind the rifle range butts. Influencing the decision to establish the “Ottawa Air Station” at Rockcliffe was the emerging thought that aerial photography could be the way to satisfy the exploding demand for accurate maps. The site was readily accessible, near government facilities, and the terrain was varied, providing areas of land and water with diverse elevations suitable for photographic experiments within a small radius of operation.

Two aircraft, both two-seaters from the Imperial Gift, were used on the tests from Rockcliffe: a 130 hp Clerget-powered Avro 504K and a Bristol F2B Fighter with a 270 hp Rolls-Royce Falcon III engine. Aircraft vibration was a real problem, compounded by the practical difficulty of maintaining straight and level flight for prolonged periods. Effective communication between pilot and cameraman was essential but usually proved impossible due to engine noise and lack of radios. Hand signals supplemented by handwritten messages, or, on occasion, pulling a string tied to the cameraman’s wrist, were the only options.

Even when photographs were successfully taken with the frustratingly slow film of the period, “matching” their edges to make a mosaic was a huge problem. Virtually every photograph had to be individually “rectified” to correct for tilt, vibration, and variations in both the aircraft and height of the ground. To do this, enlarging cameras were mounted on gimbals and swiveled to bring every photograph to the same scale.

The results were encouraging enough to continue experiments. With some enthusiasm, a system was developed to rotate the camera backwards during the minimum one-second exposure necessary, even on a sunny day, but this was too complex, heavy, and cumbersome to be practical. So other answers were sought.

Ellwood Wilson, Chief Forester of the Laurentide Company Limited, an early pioneer in the St. Maurice River watershed north of Trois-Rivières, was among the few foresters of the period to recognize the need for forest management. He saw aircraft as the means of both identifying forest resources and protecting them from fire. The Curtiss HS-2L flying boats in storage at Dartmouth, Nova Scotia, attracted his attention.

Through the St. Maurice Forest Protective Association, he arranged to borrow two of the single-engine, open cockpit biplane flying boats. Pilot Stuart Graham and engineer-photographer Bill Clarke photographed the St. Maurice River during October 1919 from Lac-à-la-Tortue.

Not surprisingly, the founders of the Alpine Club of Canada had long understood the value of an elevated viewpoint. They would haul equipment up a mountain, accurately establish its position, photograph all around (weather permitting), clamber down, and repeat the process up another mountain in sight of the first.

The gaps between established points would be filled in from the photographs. This would be repeated, again and again, until winter closed in or funds ran out—tedious, labour-intensive, expensive, and dangerous. A process known as triangulation survey was the standard method. Surveyors wanted a better way of doing the job. Their prayers were answered by the HS2L combined with the knowledge generated by the pioneers and the techniques developed at Rockcliffe.

Vertical photography, with each negative covering only a small area, about 180 by 120 metres, required inordinate skill to fly a straight “line” and to overlap the photos by just the right amount. Wouldn’t it be nice to take “obliques”, covering everything as far as the horizon? But correction of the perspective distortion was a prohibitively difficult job. Canadian Engineer R.B. McKay, and Professor H.L. Cooke from Princeton University, perfected a procedure for transferring oblique photographs to topographical format. Their system – known internationally as The Canadian (High Oblique) Method – was used for many years instead of the time-consuming procedure of drawing individual perspective diagrams were created for each photograph. A series of 100 “thick transparent celluloid sheets” were engraved with grids comprised of lines converging toward the horizon and parallel lines at right angles to the camera. An appropriate grid was selected and superimposed over each photograph. Features shown at the intersection points were then transferred to plotting sheets divided into squares. Simple! But, as always, there was a “but”!

The photographs were useless unless the mapmakers knew where they were located. This required at least two ground positions to be precisely established by latitude and longitude for each series of photographs. To do this, surveyors had to take sun or star sights from the ground. During the 1920s, the air force relied on civilian surveyors for this job and to navigate on long trips. Pilot R.C. Gordon noted in The Roundel (February 1948) that these rugged individuals “enjoyed their work, seemed to have a great capacity for living among mosquitoes, and ate and slept comparatively little.”

As the years progressed, essentially the same procedures were used. Aircrews gained the benefit of closed cockpits but still had to live in tents. Cameras and film improved tremendously. Private enterprise took up the challenge, and there was some criticism of the air force continuing what was seen as a commercial operation. Aerial photography of Canada, however, came to an end in 1939 as the RCAF devoted itself to more serious matters.

In 1945, it started up again, but this time with the benefit of aircraft developed during the war. Four-engined Lancasters and speedy Mosquitoes replaced the single-engined Vedettes, Fairchilds, and Bellancas. Most of these aircraft flew out on photographic missions from Rockcliffe. The library of photographs expanded to some six million, stored at the National Air Photo Unit on Booth Street. Anyone born in Canada should be able to find an aerial photograph of their birthplace—perhaps taken even before they were born.

The between-wars heroes gave Canada a lasting legacy of aerial photographs, used extensively today by historians, town planners, and geographers. Not so visible are other legacies:

1. The economic benefit of aerial photography for map-making justified the maintenance of an air force during the Depression years. The RCAF expanded during World War II to become the fourth-largest Allied air force, and the senior commanders were experienced photo pilots of the 1920s.

2. Mechanic-photographers flew with the photo pilots and repaired the aircraft on the shores of isolated lakes after all-too-frequent breakdowns. These “can-do” non-commissioned types knew how the system worked and were the backbone of the British Commonwealth Air Training Plan, which trained over 130,000 aircrew during World War II. Many of them rose to senior rank, and some commanded training stations.

3. Air Force specifications for photographic aircraft launched the Montreal shipbuilder Canadian Vickers into aircraft design and manufacturing. Canadian Vickers evolved into Canadair, which became Bombardier Aerospace, one of the world’s leading aircraft manufacturers.

4. Techniques developed for photography matured into Canada’s current expertise in remote sensing from aerial and world-orbiting satellites.

5. Aircrews of the 1920s also initiated aerial forest fire-fighting procedures now used throughout the world, in which Canadian aircraft play a major part.