The Eccentric Engineer: Koehler’s Genius Design of the Depressing Trolley


This is the story of how a German engineer and artist helped the British win the last battle of the American Revolutionary War.

In the early days of September, 1782, the greatest action of the entire American Revolutionary War was about to begin. Although the Battle of Yorktown, which sealed the independence of the United States, took place nearly a year before, the war was not quite over and this groundbreaking battle would have a number of unique characteristics. First, not a single American was in it, and second, it wasn’t in the New World, but around Gibraltar in the Mediterranean.

When the Revolutionary War broke out, the Americans had found themselves with unexpected allies in the form of the “Bourbon Alliance”, a combination of French and Spanish powers whose interests had as much to do with British control as with the liberation of American settlers. Thus, with the fighting in America nearly over, the greatest engagement of the war had yet to begin.

This gave George Eliott, the British governor defending Gibraltar, a problem. It had been besieged by Bourbon allies since June 1779, but the Royal Navy had always managed to break through the naval blockade and resupply its garrison. Now the Bourbons, realizing they were unlikely to starve the garrison, had decided on a full frontal attack, ranging from 65,000 troops, 47 ships and 10 floating batteries against the 7,500 men and 12 gunboats of Elliott.

Of course, anyone who knows Gibraltar can tell you that Eliott had a huge advantage. The Rock, located above the Spanish plain, was a fortress and had also been heavily fortified. While the Spanish and French had stayed far back to their own lines, this gave the British a clear line of fire, but with 65,000 troops now approaching from land and sea, Eliott had a problem – his guns.

Eliott’s guns were mounted on the usual garrison cars, with a rectangular frame mounted on four small wheels or “trucks”. They were great for shooting horizontally, like in a naval broadside, but once the enemy got too close to the bottom of the Rock, they became useless.

It was possible to wedge the carriages so that the guns could point down the cliff, but this had two serious drawbacks. First, the barrel had to be fixed in sight of the enemy and could not be removed for reloading. Second, when the gun fired at this angle, the recoil caused the whole carriage to leap into the air, damaging the trucks, the guns, and the men trying to fire them.

It was then that Lieutenant George Frederick Koehler of the Royal Artillery came to the rescue. Koehler was an artist and engineer whose father had emigrated to England from Bavaria. Finding himself caught in the siege, he set about solving Eliott’s gun problem and finally presented the governor with “Koehler’s depressing cart”. Although it may have looked like a vehicle to carry a defeated Eliott from his doomed fortress, it was, in truth, his savior.

Koehler’s depressing car was a gun mount that allowed guns to fire downhill. He wasn’t the first to come up with this idea, but his combination of two unique systems made it the first to work.

The first element of Koehler’s design was to hinge the front of the carriage on an iron spindle, allowing the gun to be pointed downward. Provided the barrel was loaded horizontally and heavily padded to prevent the load and bullet from rolling, the barrel could then be pointed downward at almost 50 degrees.

Then to solve the recoil problem. Koehler invented a sliding bed on which the barrel sat, allowing it to slide back and forth. When the cannon was fired, the gun fired back on the bed, but the car itself stood still. This simple device turned out to be the precursor to the recoil system used on just about every artillery piece since.

This “depressing cart” also had two other advantages. As the carriage did not need to be strapped in place, the gun could be reloaded from the safety of the pillboxes and, should the defenders ever need to fire uphill, the gun would simply be reversed onto the carriage allowing for a position of upward shot of 45 degrees.

Of course, as with any great military development, the proof comes in battle. After more than three years of siege, the “great assault” of the French and Spanish began on September 13, 1782 and proved a disaster for them. With the enemy driven from the Rock, Admiral Howe was able to fully resupply the garrison and the French and Spanish finally lifted the siege, ending the last action of the American Revolutionary War.

Sign up for the E&T News email to get great stories like this delivered to your inbox every day.


Comments are closed.