After decades of obscurity, military balloons are enjoying a revival. They come in two main forms: tethered aerostats and untethered high-altitude balloons.
Aerostats are tethered blimps that operate between three and five kilometres up. They can lift sensors to detect low-flying threats such as missiles and drones that leak through conventional radar coverage, and they can serve as signal relays. They cost far less than airborne warning and control aircraft (AWACs) and can remain on station for weeks.
America's JLENS programme, designed to detect cruise-missile threats around Washington, involved two aerostats floating 3km up, each carrying a radar weighing more than three tonnes capable of seeing 550km. It was cancelled after one escaped its tethers in 2015 and floated nearly 150km across Maryland and Pennsylvania. Despite that setback, the US Army signed a deal worth $4.2bn in 2025 to upgrade its aerostat fleet. America's Customs and Border Protection agency also operates aerostats along the Mexican border to monitor trafficking routes, and another flies above the coast of Puerto Rico to detect drug-carrying drones and small boats.
Poland is buying four American aerostats for an early-warning radar network to detect Russian missiles and aircraft. Israel has deployed aerostats along its border with Lebanon to warn of incoming rocket fire. Ukraine is using them as signal relays to enable its drones to fly longer distances.
Untethered high-altitude balloons float in the mid-stratosphere, typically 24-37km up—well above commercial aircraft but far closer to Earth than satellites in low orbit (160-2,000km). Their lower altitude allows higher-quality imagery than most satellites, and they can loiter over areas of interest rather than whisking past. Some modern balloons use artificial intelligence to predict and ride wind currents. Payloads rarely exceed 30-40kg, but advances in miniaturisation have revitalised their usefulness. They emit little heat or sound and use passive sensing, making them difficult to detect.
In February 2023 an immense Chinese surveillance balloon, carrying equipment in a body the size of a bus, drifted across America for days before being shot down by a fighter jet. China has also floated more than a hundred surveillance balloons over the Taiwan Strait.
Military ballooning began soon after ballooning's invention in France in 1783. In 1794 the French tethered a hydrogen balloon above a battlefield to spy on Austrian manoeuvres. Reconnaissance balloons saw action in the American civil war and the Franco-Prussian war (where they carried messages out of besieged Paris). Both sides used them in the first world war. By the second world war aircraft had supplanted them, and in the 1960s satellites rose to prominence.
The One Big Beautiful Bill, a tax-and-spending measure passed by America's Congress in July 2025, included $50m earmarked for experimental stratospheric balloons.
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