Videos posted to Russian and Ukrainian social media show that Ukraine has mated the breakout technology of small, low-cost quadcopter drones with a classic weapon of antiquity and the Middle Ages: spiky caltrops designed to be scattered in the path of enemy forces.
While Ukrainians had already been incorporating caltrops into trapped and/or fortified defensive areas, footage showed civilian-style quadcopter drones scattering thousands at night along vital roads in Russian-occupied territory used for resupply. The following day, wheeled vehicles immobilized by the tire-deflating caltrops became sitting ducks for subsequent air or artillery strikes. Even an immobilized vehicle that gets recovered is at least temporarily rendered unavailable and taxes maintenance capacity.
Perhaps the best indication that Ukraine’s caltrop tactic is proving effective is that Russian social media posts are complaining about it:
“Now the Armed Forces of Ukraine are actively dropping such ‘thorns’ on the roads used by our troops. According to their plan, after a puncture, the car stops and is destroyed by artillery fire or kamikaze drones.”
The poster says that his Tiger infantry mobility vehicle ran over caltrops, but managed to remain useable even with one tire completely destroyed.
Another Russian, seemingly a mechanic, bemoans in a social media video:
“Our favorite Gaz truck. First mission, first combat loss. [The caltrop] destroyed the wheel, they barely managed to get out. They drop these things from drones. Two URALs [most likely Ural-4320 6x6 medium trucks] with no wheels, and a GAZ-66 [4x4 truck] with no wheels arrived today.” Pointing to one of the Urals, he continued “This was supposed to be our warhorse, our savior. Two wheels lost in two missions.”
Several other Russian posts show use of caltrops to damage Russian tires.
Ukrainian use of caltrops dates back to the early days of the war. In one notable example, blacksmiths working for ‘Art of Steel’—a company specialized in fabricating medieval armor for reenactors—began mass-producing caltrops presumably deployed by traditional terrestrial means. These caltrops with six-inch nails were chained together, making them easier to remove if needed.
Giant caltrops were also seen being concealed under soft soil in ditches to impede potential Russian attacks along Ukraine’s border.
The idea to combine vertical-lift drones with caltrops appears to predate Ukraine’s battlefield use by five years when a civilian DJIA Matrice 600 drone was showcased spraying caltrops at a Chinese exhibition in 2019.
Beside the traditional iron spike caltrops, Ukrainian forces also employ caltrops made of twisted rebar, and may even use a configuration made of two cross-cutting triangles.
Caltrops: ancient weapons with modern uses
Caltrops are typically made of conjoined iron spikes—usually, they have three points balancing against the ground with the fourth oriented upwards to pierce the foot (or hooves, or tires) of unsuspecting enemies. Historical records show that they have been used in warfare for at least 2,500 years. And due to their simplicity, armies that fell afoul of caltrops were quick to adopt their use in subsequent conflicts.
Early caltrops had wooden spherical cores through which four spikes protruded. Their primary purpose was to help infantry disable the mobility and momentum advantage of cavalry, chariots, and even war elephants. The hooves of cavalry were particularly susceptible to harm, but sandal-wearing infantry were at risk as well. Besides the immediate hobbling effect, piercing injuries inflicted by caltrops are likely to become dangerously infected absent the intervention of modern medicine.
The first recorded use of caltrops is the Battle of Gaugamela in 331 BCE, during which Persian King Darius III allegedly strewed the ground with ‘crow’s feet’ to foil the forces of Alexander the Great—at least, as claimed in a history written five centuries later. Thereafter, various Greek principalities used caltrops as defensive obstacles to deter enemy attacks, a device copied by the Romans. The Greeks and Romans called them tribolos or tribulum respectively. Roman writer Vegetius described caltrops as being a highly effective counter to formerly feared scythed chariots.
Caltrops again played a major role in the Battle of Nisibis (217 AD), in which the Roman forces of inexperienced Emperor Macrinus battled a Parthians army seeking to avenge a treacherous attack by Macrinus’s predecessor. When Macrinus’s javelin-armed light infantry was compelled to fall back by Parthian heavy cataphract cavalry (supported by horse archers), they left behind a dense field of caltrops that broke up the Parthian cavalry charge. This allowed Roman infantry to bog down the Parthian cavalry in three days of fighting, which concluded with a truce and financial concession by the Roman force.
Caltrops impaired another Persia-based force in the Battle of Jalula in the year 634. This time, the Sashanids under Yazdgard III used caltrops to block passage to and from the Arab-held fortress of Jalula. Arab forces pretended to flee—and then pounced as the Sashanid troops began clearing lanes through the caltrops. The routed Sashanids suffered heavy casualties fleeing through their own caltrop fields.
By the Middle Ages, caltrops had spread from the Middle East to Europe and East Asia, with the English coining the term ‘caltrop’ in reference to the thorny star thistle plant. The design was simplified by removing the central wooden ball in favor of hammering together two twisted strips of iron. They proved an important method for helping infantry and archers stave off elite heavy cavalry.
At the Battle of Bannockburn in 1314, Scottish forces under Robert Bruces used a combination of spiked pit traps and caltrops to break the momentum of Edward II’s charging English knights. The maimed, disoriented and even dismounted shock cavalry was then dispatched by Scottish pike formations known as schiltrons. Bruce’s victory ultimately forced the English king to recognize Scottish independence.
Bruce had been advised to use caltrops by clan leader Malcom Drummond—leading to the Drummond clan incorporating caltrops in its coat of arms. Indeed, the caltrop’s military significance led it to be adopted in the heraldry of noble houses like Stirling, and even modern military units (notably the U.S. 3rd Marine Division and the U.S. Army’s III Corps.)
The English learned from the experiences, and deployed a barrage of caltrops to shield their longbowmen from charging French knights in the Battle of Crecy, then began stringing together caltrops on nets for use against each other in the War of the Roses—particularly the first major battle at St. Albans (1455).
China’s Chin dynasty purportedly deployed a 30-mile-deep belt of caltrops in front of Pei Kou fort to stop Genghis Khan’s Golden Horde in 1213. However, a Mongol blockade successfully starved the garrison to eventual defeat. The subsequent Yuan and Ming dynasties devised ‘exploding caltrops’—spiky balls filled with gunpowder.
Japanese armies also employed both iron caltrops (makibishi) and ‘organic’ tennenbishi adapted from dessicated water chestnut seed pods—also known as ‘water caltrops.’
Subsequent centuries saw sporadic use of caltrops; for example, Leonardo Da Vinci drew schematics for catapult artillery to launch containers intended to spray caltrops in front of enemy armies. English colonists sailed to Jamestown with caltrops in anticipation of hostilities with Native Americans. In India, large caltrops were devised specifically to injured war elephants. Caltrops were also deployed by Russian troops against British cavalry during the Battle of Balaclava (1854), and even at sea, caltrops were employed to give boarding parties a nasty surprise.
Ironically, the gradual motorization of land armies in the 20th century actually gave caltrops a new lease on life: sabotaging the tires of wheeled vehicles. Thus, U.S., British, and German special operations forces in World War II all employed caltrops as sabotage weapons. Caltrops devised by the U.S.’s OSS intelligence service had a hollow openings in the pins so the spikes didn’t self-seal the puncture holes in tires.
Caltrops also had applications with—and against—aircraft. German warplanes (Stuka, He-111, Ju-88 and Me-110) bombed Allied airfields and roads with cargo munitions stuffed with 1,000 to 1,500 pyramidal ‘crow’s feet’.
Intended to always fall with a point upwards, in practice, one of the sharp tips often burrowed into the ground and leaves the flat base pointing upward. But they were not wholly ineffective. In a letter to the Washington Post, U.S. Army Air Force pilot L. Prouty recalled encountering caltrops while landing at Algiers in a Model 18 passenger transport in November 1943:
As I circled the small base, the control tower called my attention to the fact that an aircraft was burning on the side of the active runway and that I would have to land on the other edge. There were fire trucks and an ambulance near the burning plane. I chose my touchdown point carefully and slowed the Lockheed Lodestar to its landing speed. I had not yet touched the ground when the right tire exploded. We had hit the razor-sharp tip of a caltrop just at touchdown. With the bad wheel on the sandy edge of the runway and the left wheel on the tarmac, I got the plane stopped without too much more trouble.”
The emergency crews had their hands full and could see that we were not in big trouble. One of the officers came out and informed us that on the previous night a few German bombers had covered the base with the small metallic weapons.”
The air-dropping delivery method attracted U.S. military interest. For Operation Tack on Feb. 4, 1951, U.S. C-47 cargo planes flying at dangerously low altitude (10-20 feet high) at night sprayed eight tons of 1.5” roofing nails and caltrops with tire-puncturing barbs (known as ‘tetrahedrons’) over major highways used by Chinese and North Korean supply trucks. The following day, warplanes blasted 28 trucks immobilized by the caltrops and nails (though a news report claims a higher toll of 65 vehicles). This compelled Communist forces to send scouts on foot ahead of vehicle convoys to detect caltrops, slowing those convoys down.
It’s unclear how frequently this method was used again, however. A U.S. Air Force museum exhibit states this “…concept proved to be impractical and was discontinued.” Yet the same method was employed against Viet Cong and Vietnamese supply lines on the Ho Chi Minh trail during the Vietnam War. Vietnamese guerillas were also known to deploy caltrops to sabotage airbases and bring convoys screeching to a halt for ambushes.
Caltrops also re-emerged as anti-personnel, deployed by UN forces to hinder Chinese human wave attacks during the Korean War. And more recently, caltrops (or “jack rocks”) have been used by civilians barring access to factories in labor disputes, and by protesters or criminals seeking to disable law enforcement vehicles (a tactic portrayed in the gangster film Heat.)
The caltrop’s physical configuration is also observable in anti-tank obstacles, like the ‘Czech Hedgehogs’ arrayed at Normandy during the D-Day landing. But while they serve an area denial role, such easily-spotted obstacles function in a fundamentally different way than a caltrop.
More comparable in function, but not in form, are the ‘spike strips’ (or Tire Deflation Devices) used by modern militaries in vehicular barricades or checkpoints. Spike strips have the advantage of being easier to safely recover than caltrops liberally sprayed over a wide area, which pose a similar long-term ‘contamination’ problem to land mines.
Ukraine’s use of drone-dropped caltrops in the 21st century reflects a new and more offensive deployment method, much as drones and rocket artillery are also being used in the war to reactively deploy minefields on supply roads well behind enemy lines. Rocket-launching ISDM Zemledeliye remote minelaying systems, each of which can scatter up to 600 anti-personnel mines in across a football-field sized area up to 9 miles away, appear to have substantially impeded Ukraine’s 2023 counteroffensive by re-mining corridors that had just been cleared of mines.
While caltrops aren’t as deadly as mines, Russian complaints offer compelling anecdotal evidence that they can cause extensive damage and delays to motor transport—particularly now that drones and artillery are more capable than ever at finishing off exposed, immobilized vehicles.
Sébastien Roblin has written on the technical, historical, and political aspects of international security and conflict for publications including 19FortyFive, The National Interest, MSNBC, Forbes.com, Inside Unmanned Systems and War is Boring. He holds a Master’s degree from Georgetown University and served with the Peace Corps in China. You can follow his articles on Twitter.
