Happy July 4th to all of Military History Now’s American readers (and there sure are a lot of you!). In honour of the United States’ 237th birthday, we thought we’d re-blog an item from June of 2012. Up the rebels!

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SOME ARMIES have been ground to a halt because they’ve run out of gasoline. Others have been sidelined for a lack of warm clothes or food. For the Continental Army in 1775, a critical shortage of gunpowder was the problem.

In fact, gunpowder was so scarce it actually threatened to end the American Revolution before it began, according to historian Michael Stephenson in his fascinating 2007 book Patriot Battles.

Stephenson describes how at the war’s outset, American general John Sullivan reported that had the British known how desperately short of powder the colonists were, they could have crushed the entire rebellion in one stroke. In fact, according to one eyewitness, when George Washington discovered that instead of the required 400 barrels of powder needed to supply his army, he could expect fewer than 40, the future first prez was so distraught he was unable to utter a sound for the next half hour. While certainly there was plenty of gunpowder in the 13 colonies at the time — the problem for the Continentals was in finding and procuring it.

In the 18^th Century, gunpowder was made using a longtime recipe that called for 15 percent charcoal, 10 percent sulphur and 75 percent potassium nitrate (also known as saltpetre). The first two substances were abundant in America, but it was the final ingredient, potassium nitrate, that was hard to come by.

A byproduct of decomposing organic matter, saltpetre could be extracted from animal droppings. In a pinch, it could be sourced from human waste — the urine of those who had consumed booze was particularly effective. Thankfully for those in the gunpowder business, the all-important ingredient could also be recovered from tropical soil rich in nitrates from decaying plant matter. While some of the southern American colonies enjoyed conditions favourable for the production of potassium nitrate, at the time of the revolution, America had virtually no domestic gunpowder industry. Instead the colonies relied on imports from Britain, but later had to get their supply from Europe or French and Dutch colonies in the Caribbean. The British on the other hand had a well-established global trading network and could obtain saltpeter comparatively easily.

So just how bad was the powder shortage for the new American army? Stephenson reported that in 1775, there was only enough powder on hand to supply soldiers of the Continental Army about 20 cartridges per solider! That might last about 10 minutes on the battlefield. Realizing this, the newly established American congress organized a hasty program to produce the substance domestically.

Building the capacity, particularly the ability to generate potassium nitrate, would take time though. In the interim, the Continental Army would have to husband its supplies carefully. This shortage became an all-consuming obsession for the rebellion’s leaders. John Adams wrote in 1775 that the production of saltpetre was never far from his mind.

Eventually, production was ramped up in the southern colonies when it was realized that the soil left over on the barn floors of tobacco plantations was rich in nitrates. One barrel of it mixed with ashes and water and then boiled and refined could produce the saltpetre needed for nearly a pound of gunpowder.

According to Stephenson, by the end of 1777, more than 50,000 tons of gunpowder had been manufactured for the Continental Army, but even that wasn’t sufficient. In fact, domestic production only accounted for a tenth of the gunpowder used by America during the revolution. The balance being delivered by French, despite the British blockade of the colonies.

John Adams wrote that had the Royal Navy’s cordon around America been effective enough to prevent the French from supplying the colonies with gunpowder, the rebellion might easily have failed and America might have remained in British hands.