It's an epic story that spanned an ocean, with a cast of thousands and the future of western democracy at stake. The vast tale of the Battle of the Atlantic holds enough history to make more than a few full-length films. Derek Sarty's design challenge was to reduce this story, in all its complexity, to one small, stamp-sized frame.

The war at sea was the longest battle of the Second World War and, in the harsh waters of the North Atlantic, Canadians made a crucial contribution. The Allied war effort depended on convoys of supply ships that crossed these stormy seas, stalked by enemy submarines. Early in the war, the Royal Canadian Navy began sailing with the convoys to protect these vital supply ships. Outnumbered and ill equipped, our naval forces succeeded in keeping the sea lanes open, but at a high cost. By the war's end, 22 Canadian naval ships had been lost, and more than 4,000 Canadians had died, including 2,000 RN, 750 RCAF and 1,650 Merchant Marines.

Each year we remember their sacrifice on Battle of the Atlantic Sunday, the first Sunday in May. For this year's commemorative ceremonies, Canada Post is issuing a single domestic rate (50¢) stamp that portrays the war at sea in vivid period photographs.

Sarty selected these images from the extensive files of the Maritime Command Museum in Halifax. "Most of the photos from this period were taken by amateurs on duty in the roughest conditions imaginable, so they're often unfocused, grainy and scratched - of little use when creating a stamp," he says.

The images Sarty found he could use were professionally scanned from original black-and-white photographs in the collections of Library and Archives Canada and the Marcom Museum. These high-quality digital versions were cleaned, sized, adjusted and colourized. Then Sarty assembled them into a composite image that plunges the viewer into the midst of a harrowing high-seas battle.

In the sky, the coastlines of eastern North America and western Europe mark the boundaries of the threatre of operations," Sarty says. "In the convoy of vessels on the horizon, a supply ship has just been torpedoed. Survivors from another torpedoed ship struggle in life boats and in the sea. A sailor lookout is on high alert as a Canadian Navy corvette springs into action. But a German U-boat has already set its sights on its next target, the corvette."

To heighten the visual drama, Sarty added fields of colour in nautical tones reminiscent of the period, which also suggest the harsh conditions of the North Atlantic.

Assembling this composite image required weeks of fine detail work. For example, Sarty digitally close-cropped the entire corvette, outlining each wire, bump, knob and figure. "I know every detail of that ship intimately now," he laughs. "But the effort is worthwhile. With stamp designs, it's important to err on the side of excellence."