David McDonough gave a stout defence of the Air Warfare Destroyer on this blog. In several respects it’s a superior platform to our existing fleet and some proposed alternatives—namely, the smaller, cheaper ships suggested by Hugh White. However, close focus on the operational task of that AWD and the strategic objective underpinning that task is essential.

I’ll sidestep the important ship survivability question to tackle another important objective of our naval forces. James Goldrick rightly highlights the importance of protecting maritime trade. However Andrew Davies and Mark Thomson cast doubt on whether navies will ever be sufficient to protect trade, due to the falling relative size of naval fleets.

That poses a question: if merchant fleets are now so vast, and naval fleets so small and increasingly shrinking, why is seaborne trade still safe compared to the centuries of the Age of Sail? Today the International Maritime Organization’s monthly and annual reports count a few hundred pirate attacks annually, but only a few dozen hijackings succeed (33 in 2012), and it’s very seldom that crew or ships remain missing. Land raids on ports are non-existent, and condemnation from nation-states is universal. In contrast around the period 1803–1812 the USN understands that 1,500 American merchant vessels were seized by England and France, around 10,000 American sailors kidnapped and enslaved in the service of the Royal Navy. One thousand, five hundred English ships were captured mostly by American privateers during the War of 1812 that followed, and Rear Admiral Cockburn terrorised towns in the Chesapeake. If Andrew and Mark are correct, increased naval presence alone can’t have made shipping routes so secure. Perhaps another factor is at play, and I’d argue that technological change is the key.

Three hundred years ago wooden ships fought at extremely close range. Decisive battles often ended in a melee, where the ships were drawn together, one crew overpowered the other, and took the ship as a prize. Ideally some broadsides would have killed many of the opposing crew before boarding, but the battles generally concluded with stiff close-quarters combat on the decks of the ship. As such, ships rarely sank. Instead, the prize was sailed back to port by its captors, along with its cargo and prisoners. The ships were then repaired, and redeployed.

Consequently there was an economic incentive to engage in naval warfare, including attacking merchant ships. Not only did the victim suffer a material loss, the aggressor gained a direct benefit. The opportunity to surrender when defeat seemed certain was another corollary, often exercised by merchants attacked by naval vessels, or heavily armed pirates or privateers.

Fast-forward to WWI. With conoidal explosive shells, concentric forged steel gun-barrels, submarines, planes and torpedoes, anti-shipping weapons were long-ranged and lethal. The first shots were fired from miles rather than yards away. Steam power and iron hulls made a difference too. Blasting away masts and rigging effectively immobilised a ship while leaving its wooden hull afloat. The equivalent attack on the boiler and turbines meant initially penetrating deep into the heavy iron hull below the waterline, which inevitably sank first.

Overall, technological developments had transformed naval warfare. In the Age of Sail, ships were hard to sink, but easy to steal. In the 20th century the opposite was true. If a ship refused to surrender, it was hard to overpower without sinking it. But sinking a merchantman by surprise with a torpedo from a submarine was relatively easy, cheap and effective, as Germany showed during WWI. The maritime establishment of 1917 were appalled, but couldn’t reverse the paradigm shift. Stopping shipping meant sinking vessels, and generally by surprise.

This links closely to the peace of our oceans today. Two hundred years ago state naval powers routinely sponsored private citizens to attack and steal rival shipping with or without a formal state of war. Now such harassment or theft seems unthinkable between nation states. And it’s not because we have a naval ship escorting every merchant. It’s because an escalation leaves both parties’ merchant fleets sunk, and no-one profits.

Consequently it’s possible that navies don’t keep merchant ships safe by protecting them directly from attack. Instead they credibly threaten lethal and overwhelming retaliation on other merchant ships. Long-range, powerful weapons that can deny access to the most advanced naval ships hold the maritime equivalent of a nuclear threat over un-armed commercial trade. We are living in an age of Mutually Assured Economic Destruction (MAED). Like the infamous MAD doctrine of the Cold War, it’s remarkably stable and effective at deterring any aggression against merchant ships, despite the horrific cruelty necessitated if it were exercised.

If this theory has merit the implications could be substantial for navies. There will still be a need for them and their surface vessels. However, the types of ships and functions we expect of them might change. In particular, the expensive Area Air Defence capabilities of the AWD might not be justifiable on the grounds of protecting trade. Ironically, some relatively cheap but still lethal ship-sinking platforms, (like basic diesel submarines, or even lowly missile corvettes or swarms of speedboats) could be exactly what we need.