In a world marked by growing geopolitical tensions, security concerns are taking on increasing importance - often relegating environmental protection to second place. And yet, far from always being antagonistic, the issues of defence and ocean preservation have great potential for synergy. The seas and oceans, as strategic, ecological and economic areas, are the focus of multiple interests. This text explores the possible synergies between these areas, highlights the benefits of an integrated approach capable of reconciling sustainability, security and defence, and suggests ways of stimulating them.