Submarine Day

What the day is

Submarine Day is observed on March 17, generally linked to the 1898 demonstration of John Philip Holland's submarine, the design that persuaded navies the idea was practical.

Origin and background

Submerging is the easy half. A submarine dives by flooding ballast tanks with seawater until it is heavier than the water it displaces, and surfaces by blowing that water out with compressed air. The principle was understood centuries before anyone built a usable boat.

Air was the constraint that actually mattered. A sealed crew compartment runs into two separate problems, and only one is obvious. Oxygen is consumed, but carbon dioxide accumulates, and the carbon dioxide becomes dangerous well before the oxygen runs short, which is why early crews were incapacitated while air still seemed breathable. Modern boats solve both independently, generating oxygen by splitting seawater electrically and scrubbing carbon dioxide chemically out of the atmosphere. Nuclear propulsion removed the other limit by ending the need to surface for air to run engines, so the endurance of a modern submarine is set by food and by crew rather than by the boat.

Holland's contribution was combining an internal combustion engine for the surface with electric motors on batteries for submerged running, which became the standard arrangement for half a century.

The other defining problem is navigation without radio, which does not penetrate seawater usefully. Submarines rely on inertial navigation, tracking every acceleration from a known starting point to calculate position without reference to anything outside, and communication uses very low frequency transmissions that carry little information slowly.

Depth is limited by hull compression, and the crush depth of a boat is a closely held figure for obvious reasons.

How to take part

• Visit a preserved submarine, which conveys the cramped reality better than any description.
• Read about carbon dioxide rather than oxygen as the real limit.
• Look up how inertial navigation works without any external reference.
• Note how much of the design is about air rather than water.