Hundreds of years before the Manhattan Project, an Italian weapons expert in the pay of the English government created the 16th century equivalent of a tactical nuclear weapon.

Some of the largest non-nuclear explosions on record — in Halifax, Nova Scotia in 1917, Port Chicago, California in 1944 and Texas City, Texas in 1947 — involved huge accidental blasts at harbors and aboard ships.

But what if a similar explosion occurred by intent rather than accident? A really powerful bomb, as big as a ship, could change history.

A bomb disguised as a shipping container — mixed in with the great volume of traffic and cargo passing through a major seaport — makes for a scenario that keeps U.S. Homeland Security officials awake at night. An entire ship converted into a floating bomb makes for nightmare fuel.

The really scary part? It wouldn’t be unprecedented.

Hundreds of years before the Manhattan Project, an Italian weapons expert in the pay of the English government created the 16th century equivalent of a tactical nuclear weapon. After Federigo Giambelli’s offer of services to the Spanish court received a lukewarm reception, he moved to Antwerp and settled down.

In 1584, Dutch separatists began a bloody 80-year-long war of independence from the Spanish Empire that England was only too happy to encourage. The Duke of Parma besieged the rebel city Antwerp with all the might of a superpower. Imperial troops lashed together ships to make an 800-foot-long wooden bridge barricading the Scheldt river.

Antwerp would have starved, but Giambelli determined otherwise. As he prepared the city’s defenses, he offered his talents to Queen Elizabeth I and came to the attention of her spymaster and private secretary, Sir Francis Walsingham.

To break the siege of Antwerp, Giambelli needed to destroy Spain’s wooden ship-barrier. His genius combined two newer technologies — clockwork and gunpowder — with a vessel into a terrifying new weapon.

It was the hellburner.

Huge Bomb, High Tech:

To begin with, think of a hellburner as a really big and exceptionally dangerous fire ship. Since ancient times, combustible wooden vessels feared the fire ship like no other weapon. Fire ships — worked by skeleton crews, set aflame like giant torches and set adrift upon wind and tide — could burn entire fleets and waterfronts.

But the hellburners were more than that.

The city fathers of Antwerp gave Giambelli some 32 vessels to work with. Thirty of them became conventional fire ships. The final two became the biggest bombs Europe had ever seen to that point.

Within the holds of the ships Fortyn (“Fortune”) and Hoop (“Hope”) Giambelli built giant, massive bunkers — forty feet long with brick floors and walls one to five feet thick. After filling them with two and a half tons of the finest gunpowder Holland could make, Giambelli’s workers roofed the structures with rows of recycled tombstones.

On top of that, they packed millstones and scrap around around the bunkers, decked over the giant bomb and disguised the vessels as “regular” fire ships.

The Fortyn used a conventional chemical trigger and timer — a slow-match which burned at a steady rate. The other hellburner, the Hoop, introduced a quantum leap in technology. An Antwerp clockmaker named Bory created a mechanical timer which triggered a wheelock firing mechanism. The Hoopbecame the first known pre-programmed and remotely-triggered weapon of mass destruction.

On the night of April 4, 1584, the Antwerp separatists released their fire ships into the Scheldt’s current. The Spanish troops showed little concern for the vessels approaching their positions. As the burning ships drifted onto the riverbanks and bumped into the great barricade, soldiers fended them away with pikes.

The Fortyn ran aground short of the barricade and failed to explode completely. Mistaking it for merely a noisy, unsuccessful fire ship, the Spanish forces jeered the Dutch attack. But the Hoop collided with the barrier near where it connected to the shore. Soldiers, not knowing the danger inside, boarded the vessel to put out its fires.

Then the clockwork reached its set time … and triggered the wheelock firing device. Boom.

The gigantic explosion instantly vaporized a quarter of the barricade and nearly 1,000 Spanish troops. Timber, shrapnel, rocks and body parts rained down for miles, the river surged out of its banks and the noise woke people 50 miles away. It was likely the loudest man-made bang in history up to that time.

Tactically, the hellburners had limited effect. The Dutch were so stunned by the explosion they failed to capitalize on the Spaniards’ disarray. Within months the Spanish Empire rebuilt the great wooden barricade and stepped up its siege. Antwerp fell the following year in 1585.

Incinerated in One Blow:

Strategically, though, the hellburners changed history. Giambelli escaped to Britain, likely with the help of English forces fighting with the Dutch. In a letter to Sir Francis Walsingham, English army Col. Henry Norreys extolled Giambelli and his art:

As I know you esteem men of rare gifts, I pray you to afford him your favour and to despatch him hither again if you so think good, as we may have occasion to use his service in these parts.

It’s unknown whether Walsingham and Giambelli ever met. Three years later in 1588, as Giambelli worked on a wooden barricade to defend the Thames, Walsingham received reports of a second Dutch floating bomb that destroyed ships at dock in Dunkirk. The knowledge that Europe’s master weaponeer now worked for Elizabeth unsettled the Spanish military.

The year 1588 saw Spain mount the greatest naval assault against England in history. An armada of galleons under the Duke of Medina-Sidonia, with 20,000 troops and cavalry aboard, sailed up the English Channel to meet up with the Duke of Parma’s armies in the Low Countries. The armada would escort the imperial troops across the Channel and reinforce the invasion of England.

On the night of Aug. 7, 1588, as the armada sheltered at Calais, the English launched eight fire ships into the anchorage. This time the Spanish were anything but blasé. Ships and crews swiftly cut anchor cables and hoisted sail to avoid the incoming pyres.

The vast fleet scattered and never really regrouped. The rattled armada, now shorn of anchors and tackle, failed to bring its might to bear on the English attackers. The fleet never connected with the Duke of Parma’s invasion force and wound up returning home the long way around the British Isles. Spain’s invasion of Britain never happened, with all the failure’s consequences for history.

Why did a mere eight burning ships disrupt a huge invasion? Simple — a hellburner might have incinerated Spain’s naval might in one blow. Though Giambelli apparently never built another hellburner for the British or anyone else, the knowledge that he could, and was in England, bent the arc of history.

Although the hellburner captivated 16th century military imagination, it never saw widespread use. One hellburner used as much gunpowder as an entire army or a fleet, all in order to strike one hellacious blow. Few opportunities justified such tremendous costs.

This piece first appeared in WarIsBoing here.