Bags, Belly Tanks and Bombers.

By 1957 two different concepts for aerial attack of forest fires had emerged in North America.  In some areas, particularly in the Southwestern United States,  land based aircraft were used.   In Canada, with its many lakes, water based aircaft were preferred.  The Province of Ontario became an innovator in developing water-based waterbombing systems, with the main centre being at the Ontario Provincial Air Service base in Sault ste,. Marie (now the site of the Canadian Bushplane Heritage Centre)

Carl Crossley

In 1944, Carl Crossley, an OPAS pilot stationed at Temagami, reasoned that if aircraft could be used to drop bombs upon cities in war-torn Europe, then they could be used to drop water on a forest fire.    Early expirements with a 45 gallon barrel strapped into the open front cockpit of a Fairchild KR-34 evolved into custom water tanks built the floats of a Noorduyn Norseman.   In August 1945 he extinguished a small fire near Elk Lake with his system.   Further tests followed however the promising idea was not pursued.

Bags of Water

Development of water-bombing systems shifted to the water bag method which was simpler and less expensive. Water-filled bags, each containing 3.5 to 5 gallons of water, were dropped out of the aircaft.  Later improvements added a conveyor belt to allow dropping bags out of the bottom of the aircaft in groups of eight. The first operation waterbombing with bags took place on September 9, 1950 from a DeHavilland Beaver on a fire north of Sault Ste. Marie.
This system was finally discarded because:

Roll-over, Float and Internal tanks

In the mid 1950s, Tom Cooke of the OPAS brought waterbombing back on track by developing float-mounted roll-top tanks that allowed water to be dumped in a deluge rather than a trickle to combat fires.   A cockpit lever controlled dumping and lights notified the pilot when the tank was filled.  The system was so successful that by 1960 all 35 Beavers and 8 Otter of the Provincial Air Service had been fitted with the tanks.   The Otters were also fitted with larger belly-mounted roll-over tanks.  
Eventually the external rollover tanks were replaced by built-in float tanks.   In 1971 the OPAS converted 7 Grumman CS2F-1 Trackers antisubmarine aircaft into land-based waterbombers with fuselauge tanks.
IN 1961 Canadair of Montreal began design of the CL-215.   This aircraft was purpose-built as a waterbomber from the outset with large internal water tanks and a sophisticated dropping system.

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