Warfare has been found to have detrimental impacts on biodiversity due to its long-lasting economic and social consequences. Yet, much less is known about the amount of biodiversity loss directly resulting from the use of military technology. This paper analyzes the environmental consequences of one of the largest aerial and naval conflict of the late 20st century, namely the 1982 Falklands War. The fact that the conflict was unrelated to environmental issues, did not spill over to neighboring countries, and did not relapse afterwards, allows us to circumvent identification issues that commonly affect comparative studies on the ecological footprint of warfare. As an indicator of the marine ecosystem status, we analyze population trends of king penguins breeding at the Falkland Islands, which we compare to ten other penguin colonies over a thirty-year period (1965-1995). We use the Synthetic Control Method (SCM) approach in order to build ``counterfactual'' Falkland Islands whose characteristics closely resemble those of the Falklands before the war and allows us to approximate the trends of the outcome variable in the absence of the war. Results indicate that the war has led to a substantial decrease of king penguins' breeding population: by the mid-1990s, the number of breeding pairs on the islands was approximately half what it would have been in the absence of the war. We find no evidence of lasting effects, suggesting that the population decrease is attributable to direct war mortality rather than to permanent environmental damages.