Why the U.S. Navy’s most elite sailors train with a shriveled volleyball

Cultures · Published 10 October 2026 Swipe more like this →

In short: Submarine service is a volunteer-only branch defined by extreme psychological and physical rigor. Before joining the fleet, candidates undergo specialized pressure testing in chambers where ambient air is compressed to mimic deep-sea conditions. The telltale sign of this intense environment is a volleyball that visibly collapses under the crushing pressure.

The U.S. Navy submarine force is a small but disproportionately powerful arm of the military. While submariners accounted for less than two percent of Navy personnel during World War II, they were responsible for 55 percent of Japan's merchant marine losses. Today, the force remains exclusive, comprised of volunteers who undergo rigorous screening. This selection process is so effective that submariners exhibit significantly lower mental hospitalization rates than their counterparts on surface ships.

Training for these sailors is demanding and often classified. Beyond technical schooling at sites like the Naval Submarine School in Groton, Connecticut, candidates must pass physical pressure testing. This involves a two-day course where trainees enter a sealed chamber to simulate the pressure differentials experienced at operating depths. A key part of the experience is watching an inflated ball—often a volleyball—shrink into a bowl-like shape as the air pressure inside the chamber increases. This visual demonstration highlights the extreme environment that defines the submarine service.

The evolution of the fleet has been marked by technological revolutions, most notably the 1955 launch of the USS Nautilus, the first nuclear-powered submarine. Nuclear power removed the need for frequent surfacing to recharge batteries, allowing vessels to remain submerged for months. Later, the introduction of the USS George Washington added strategic ballistic missiles, completing the nuclear triad. Today, the fleet consists entirely of nuclear-powered vessels, ranging from fast-attack submarines to massive Ohio-class platforms capable of carrying 154 cruise missiles, ensuring the Navy maintains a constant, stealthy deterrent presence globally.

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