By Rory Medcalf
Amid rapid geopolitical change at the start of the 2020s, unfolding now in the Covid-19 crisis, nuclear weapons manifest grim continuity with the previous century. Especially persistent is a capability that has existed since the 1960s: the deployment of nuclear weapons on submarines. The ungainly acronym SSBN represents nuclear-powered ballistic missile submarines: the most destructive armaments carried on a supposedly undetectable, and thus invulnerable, platform.