Convoy

Even if the privateer found a convoy and the wind was favourable for an attack, it could still hope to capture only a handful of ships before the rest managed to escape, and a small escort of warships could easily thwart it.

These submarines were only a little faster than the merchant ships they were attacking, and capable of sinking only a small number of vessels in a convoy because of their limited supply of torpedoes and shells.

The Admiralty took a long time to respond to this change in the tactical position, and in April 1917 convoys were trialled, before being officially introduced in the Atlantic in September 1917.

[3] Convoy duty also exposes the escorting warships to the sometimes hazardous conditions of the North Atlantic, with only rare occurrences of visible achievement (i.e. fending off a submarine assault).

The British adopted a convoy system, initially voluntary and later compulsory for almost all merchant ships, the moment that World War II was declared.

Only the sacrifices of the armed merchant cruiser HMS Jervis Bay and the freighter Beaverford to stall the Scheer, in addition to failing light, allowed the rest of the convoy to escape.

When the Germans detected the slow but well-protected battleship HMS Ramillies escorting the convoy, they fled the scene rather than risk damage from her 15 in (38 cm) guns.

The enormous number of vessels involved and the frequency of engagements meant that statistical techniques could be applied to evaluate tactics: an early use of operational research in war.

US Fleet Admiral Ernest King ignored advice on this subject from the British, as he had formed a poor opinion of the Royal Navy early in his career.

In the early part of the conflict, American submarines in the Pacific were ineffective as they suffered from timid tactics, faulty torpedoes, and poor deployment, while there were only small numbers of British and Dutch boats.

U.S. Admiral Charles A. Lockwood's efforts, coupled with strenuous complaints from his captains, rectified these problems and U.S. submarines became much more successful by war's end.

At the Battle off Samar, the effectiveness of the U.S. Navy's escorts was demonstrated when they managed to defend their troop convoy from a much larger and more powerful Japanese battle-fleet.

There was a real problem for the U-boats and their adversaries in finding each other; with a tiny proportion of the ocean in sight, without intelligence or radar, warships and even aircraft would be fortunate in coming across a submarine.

For both major allied navies, it had been difficult to grasp that, however large a convoy, its "footprint" (the area within which it could be spotted) was far smaller than if the individual ships had traveled independently.

If, however, an attack were thwarted by escorts, even if the submarine had escaped damage, it would have to remain submerged for its own safety and might only recover its position after many hours' hard work.

U-boats patrolling areas with constant and predictable flows of sea traffic, such as the United States Atlantic coast in early 1942, could dismiss a missed opportunity in the certain knowledge that another would soon present itself.

In the present day, convoys are used as a tactic by navies to deter pirates off the coast of Somalia from capturing unarmed civilian freighters who would otherwise pose easy targets if they sailed alone.

The word "convoy" is also associated with groups of road vehicles being driven, mostly by volunteers, to deliver humanitarian aid, supplies, and—a stated objective in some cases—"solidarity".

They are often justified because although less directly cost-effective than mass freight transport, they emphasise the support of large numbers of small groups, and are quite distinct from multinational organisations such as United Nations humanitarian efforts.

The Highway Code of several European countries (Norway, Italy, Greece, Netherlands, Germany, Austria, Switzerland, possibly more) includes special rights for marked convoys.

Large-scale evacuations for the disarming of World War II bombs are another common reason for non-governmental organization (NGO) unit movements under convoy rights.