Human Endurance in Early Submarines

Popular histories of underwater warfare frequently dwell on the technological ingenuity of nineteenth-century inventors, charting a heroic progression from crude wooden barrels to sleek steel hulls. This narrative, in my view, presents an unbalanced picture of the era. The fundamental obstacle confronting early submersible designers was not merely hydrodynamic efficiency or structural resistance to water pressure, but the severe and often lethal constraints imposed by human biology. For decades, ambitious inventors constructed sealed vessels capable of submerging, only to discover that the men inside rapidly deteriorated in the unnatural conditions of the deep. It is impossible to appreciate the evolution of underwater craft without recognising that engineering ambitions consistently outpaced the physiological capacities of their crews.

The most urgent challenge was atmospheric regulation within an enclosed space. Early innovators operated under the mistaken belief that simply providing a generous volume of trapped air would sustain life for hours. In practice, the accumulation of toxic carbon dioxide posed an acute threat long before oxygen levels fell to dangerously low levels. Even a minor rise in carbon dioxide concentration impairs cognitive function, induces severe headaches, and eventually triggers panic—a fatal reaction in an environment requiring absolute composure. Some nineteenth-century experimenters attempted to scrub the air using chemical absorbents like slaked lime, but these systems were rudimentary and unreliable. It would be an error to credit early designers with a sound understanding of respiratory physiology; they regularly prioritised air replenishment over toxic gas filtration, with catastrophic results.

Propulsion presented an equally punishing physical barrier. Before the development of compact electric motors, submersibles relied entirely on manual labour, obliging crew members to turn heavy iron crankshafts in cramped, sweltering conditions. Modern commentators frequently extol the fortitude of these sailors, yet they tend to underestimate how rapidly manual labour depleted oxygen reserves and degraded operational effectiveness. A human body engaged in strenuous physical exertion consumes up to four times more oxygen than at rest, producing a corresponding surge in carbon dioxide. In several recorded trials, crews attempting high-speed runs became completely incapacitated within fifteen minutes. The reliance on muscle power was not merely an awkward compromise; it was an inherent flaw that rendered genuine tactical manoeuvring virtually impossible.

Beyond physical exhaustion lay intense psychological strain. Confined in pitch-black, leaking hulls with no visual contact with the outside world, crews faced constant acoustic distortion and sensory deprivation. Under such conditions, even experienced mariners were vulnerable to sudden bouts of claustrophobia and disorientation. While mechanical failures certainly accounted for numerous sinkings, I would argue that psychological collapse was just as potent a factor in early mission failures. The dread of being entombed alive often led to erratic navigation or premature surfacing, undermining missions before mechanical failure could even occur.

When engineers attempted to replace human muscle with steam power in the late nineteenth century, the biological environment inside submersibles grew significantly worse. To submerge, a steam vessel had to extinguish its boilers, seal its smokestacks, and dive while residual heat radiated throughout the interior. Temperatures inside these craft routinely exceeded fifty degrees Celsius, accompanied by choking soot and scalding condensation. Some historians have described steam submersibles as a necessary stepping stone toward modern submarines, but I regard them as an unmitigated dead end. The thermal stress inflicted on crews was intolerable, turning the hull into a virtual oven that rendered sustained underwater navigation impossible.

The reluctance of traditional naval hierarchies to adopt underwater vessels during this period has frequently been dismissed as reactionary obstinacy. Senior admirals certainly denounced submarine warfare as underhanded and ungentlemanly, but it would be unfair to attribute their scepticism entirely to antiquated prejudice. Navies had a legitimate duty to assess the survivability and practical utility of naval assets. Given that early submersibles routinely killed their own crews during trials without inflicting damage on any adversary, naval commanders were entirely justified in viewing these craft as lethal liabilities rather than viable naval weapons.

It was only at the close of the nineteenth century, with the convergence of reliable electric storage batteries, internal combustion engines for surface running, and compressed air systems, that the submarine became genuinely viable. Crucially, these developments succeeded not because they introduced revolutionary hull shapes, but because they finally created an internal environment that permitted human beings to function without imminent risk of asphyxiation or heat stroke. The history of the submarine should therefore be understood primarily as a victory of life-support engineering and human adaptation, rather than a mere triumph of naval architecture.