No. We often borrow money during wartime.

According to Official Government Statistics:

    The Government generated deficits during the War of 1812, ... the Civil War [and] World War I. World War II forced the Nation to spend unprecedented amounts on defense and to incur corresponding unprecedented deficits.


IN fact, during that war, the budget deficit was, as a percentage of the Gross Domestic Product, actually about nine times higher than it is today.

Even the old WWII "War Bonds" were basically a form of government borrowing.

I also believe there were slight deficits during much of the Vietnam war.