We interviewed Guillaume Lerouge, a Paris-based defense-tech investor and partner at Hexa, being among the earliest backers of Harmattan AI, France’s first defense-tech unicorn, and Alta Ares.
Europe’s defense technology ecosystem has shifted from niche to mainstream in just a few years. Once dominated by large incumbents, the sector is now seeing a new generation of software-driven, capital-efficient startups that are increasingly venture-backed.
In this interview, Guillaume explains why he started investing before defense tech became fashionable, how deal flow really works in the sector, which areas remain underfunded, and what red flags make him walk away from a startup.
Who Are You and What Are You Working On?
I joined Hexa in September 2025 to launch an acceleration program dedicated to defense startups. We invest 500k€ in early-stage defense and dual-use startups, and provide them with 6 months of operational support to maximise their chances of success.
Earlier in my career, I worked on startup acceleration and corporate innovation programs around cybersecurity, data, and AI. I also spent time helping large organizations adopt AI internally. During that period, I met Loïc Mougeolle, who was then working at Naval Group’s innovation hub. We discussed how defense could shift from large, expensive systems to smaller, more affordable AI-powered ones.
I later joined Thales, a large international aerospace and defense company, to move closer to defense and kept these ideas in mind. I was part of their digital factory and initially led a startup program focused on cybersecurity companies based at Station F. The goal was to build strong collaborations between startups and Thales’ business units.
I also studied companies like Anduril to understand how a software-defined approach could reshape the sector. By late 2022 and early 2023, I started actively investing in new defense startups through angel networks and small funds.
What’s Important to Succeed as an Investor?
You need at least two ingredients. First, a deal flow so you are exposed when the opportunity comes. Second, you need a prepared mind. You have seen similar things before, and you can recognize when it is time to act. That part is on you. Deal flow, on the other hand, is something you can never fully control. What you can do is put yourself in the right place, ideally at the right time.
How Did Investing in Defense Tech Look in 2022?
It was early and full of uncertainty. You had to believe that there would be a real market, that startups would not be crushed by incumbents, and that they would find customers and follow-on capital.
At the same time, innovation in Europe often follows the United States with a five to ten-year delay. If you look at Anduril, they started in 2017 and were clearly significant by 2021 or 2022. Adding a five-year offset brings you to 2022 in Europe. That was when I believed strong defense tech companies would start to emerge. Helsing’s creation in 2021 fits that timeline.
In Europe, especially in France, there is often a tendency to list all the reasons a project might fail. I try to reverse that logic and ask what would need to be true for this startup to succeed. Once you answer that question, you take the leap.
Is Investing in Defense Tech Different From Investing in Other Fields?
Two or three years ago, defense tech was simpler in a sense because there were far fewer startups. In SaaS or AI, you might see hundreds of companies. In defense, there were only a handful. If you had a firm conviction, you could go deep into the sector.
That changed quickly with the war in Ukraine and broader geopolitical shifts. Today, there are many more teams and use cases, which means more time is needed to evaluate opportunities.
At the early stage, however, the fundamentals remain similar. At Hexa, we look for strong and complementary founding teams. In defense, it helps if one founder has operational experience in the military or defense industry. You also need a clear problem, a real market need, and strong differentiation.
One critical factor that is often underestimated is the go-to-market. In defense, some products have only one or two potential buyers. If they do not buy, the company fails. We carefully assess whether a startup can start with smaller operational teams, or whether it depends on convincing a single top-level decision-maker from day one.
How Do You Generate High-Quality Deal Flow for Your Angel Investments?
Early-stage investing is highly localized. You have ecosystems in France, Germany, the Baltics, Poland, and elsewhere. The easiest place to start is your own local market and understanding it deeply.
In 2022 and 2023, I was part of defense-focused angel groups and worked with a micro-fund that makes many investments each year. That model requires reviewing a large volume of inbound deal flow. Being present at Station F, one of the world’s largest startup campuses, also helped, as I could see projects early and reconnect with founders launching new ventures.
Today, Hexa is well known in France at an early stage, which makes inbound deal flow easier. The next step is to expand internationally and build a truly European defense program rather than a mostly national one.
Which Areas Do You Believe Are Still Underfunded but Critically Important?
One major area is electronic warfare, especially AI-driven electronic warfare. Ukraine has shown how decisive this domain can be, and there is still room for significant innovation.
I am also interested in less-obvious areas, such as inflatables. These could enable low-cost evasion of detection systems. Of course, I continue to watch classic areas such as low-cost long-range strike, distributed sensor networks, urban and subterranean combat, and underwater warfare. Many of these areas remain strategically vital and technologically challenging.
What Are the Main Red Flags You Look for When Evaluating a Defense Tech Startup?
The first one is limited market potential. Some projects are interesting and important, but lack a path to capturing a large or meaningful market.
The second is a mismatch between the team’s skills and the technical challenge they are trying to solve. Even a strong idea can fail if the team lacks the expertise required for a deep technical breakthrough.
The third is fragile go-to-market execution. If success depends on one or two customers or a single inaccessible decision maker, the risk is simply too high, even if the product itself is strong.
How Do You See the Defense Tech Ecosystem Evolving Over the Next Decade?
If Europe follows a path similar to the United States, we will likely see a proliferation of new defense tech companies in the coming years. Over time, that growth phase may be followed by consolidation, hopefully IPOs for a few players, and acquisitions by incumbents trying to keep pace with innovation.
Overall, I expect a more dynamic and competitive ecosystem than what we see today.
What Has Been Your Best Investment So Far, and Where Do You Expect the Next Unicorn to Come From?
The most successful project in my portfolio so far has been Harmattan AI. In just two years, the company moved from a promising idea to a highly credible and strategically positioned player, especially after its partnership with Dassault.
As for the next unicorn, it is always difficult to predict. That said, I would place a strong bet on startups working on counter-drone technologies, both in detection and interception. The demand is clear, and innovation in this area is accelerating quickly.
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