BILLY BISHOP GOES TO WAR, written and composed by John Gray in collaboration with Eric Peterson; set design by David Lloyd Gropman; lighting design by Jennifer Tipton.

With Eric Peterson and John Gray.

At Arena Stage through March 23.

"Billy Bishop Goes to War" will not add greatly to our understanding of heroism, battlefield psychology or World War I, but it is a small and welcome addition to our supply of mirth, which has been running dangerously low.

With all due allowance for the current wave of gratitude toward our northern neighbors, it would be hard to imagine a more improbable-sounding entertainment than this two-man musical about a Canadian flying ace. But there it was, anyway, on the stage of the Kreeger Theater last night, being improbably funny, rousing, schmaltzy and, in flashes, enlightening and moving.

A two-man show is only as good as its two men. Eric Peterson, who plays Billy (and an assortment of comrades, superiors, admirers and airplane engines), is a scrawny dynamo of comic brilliance whose attitude toward characters seems to be: "The less like me, the better." In the tradition of Peter Sellers, Alec Guinness and Alan Bennett, Peterson delights in impersonating haughty, strange and downright daft old ladies ond gentlemen -- an enthusiasm he is able to indulge often here.

The other man on the Kreeger state, John Gray, never rises from his piano, where he maintains a sober expression while playing and singing an agreeable score of his own composing. Together, Gray and Peterson are reminiscent of Flanders and Swann or the "Beyond the Fringe" quartet and its various spinoffs.

Of course, "Billy Bishop" has history as well as comedy on its mind, but its standards of historical verisimilitude are, to say the least, flexible. b

Billy Bishop was real and really a hero, however. In fact, if the Canadians are to be trusted with numbers, he outscored our own Eddie Rickenbacker by nearly three to one (72 planes downed versus 26). He went to France as a cavalry officer in 1915 and as this version has it, quickly decided that the muddy trenches were not the place to be. When a plane landed nearby, he noted enviously that the pilot was not only dry but seemed to be working in an environment free of both horses and superior officers.

Flying, in sum, looked like good clean work. And better still, as a helpful pilot informs Billy in the show, the brief life expectancy of the average flyer -- 11 days, he says -- has opened the field to a new class of applicant. "The upper classes are depressed by the current statistics, so they're not joining with the usual alacrity," the pilot explains. Now anyone who wants to can get blown out of the sky, even Canadians."

From "Up Front" to "M*A*S*H," the grunt's-eye-view of war and the military has become the difference in this Canadian production (imported from the Vancouver East Cultural Centre) is that the grunt becomes a hero -- a bona fide hero, and not by some comic fluke, either. "Billy Bishop" suggests that honors in war are attained with qualities not too different from those that make for honors in the insurance business -- ambition, energy, common sense, even discretion.

"When you fight, stay as calm as the ocean," runs one of "Billy Bishop's" lyrics. Following that precept, Billy returns home to security and prosperity, while the leading English pilot, Albert Ball, a romantic figure with "fire in his spine," is shot to pieces after downing a mere 43 planes.

Although filled with yarns about military foolishness, "Billy Bishop" indulges in one romantic fantasy of its own: a vision of air war as a noble and uncluttered alternative to the grim business down below.

"Oh, let us dance together in the sky," Billy sings. "Just you and I together, who knows why?/One the hunter, one the hunted/A life to live, a death confronted/Oh, let us dance together in the sky."