The first modern submarines were constructed in the 20th century, shortly before 1914. During the Anglo-German naval race the Germans built a variety of U-boats, the first of which was the U-1. The Royal Navy also expanded their navy with submarines. In smaller wars shortly before 1914 such as the Italo-Turkish War submarines were deployed but did not have any impact.

During the Balkan Wars the Greek Navy had a few submarines. Among them was the Deflin which was the first submarine to fire a torpedo. As the torpedo had little impact the targeted warship remained very much intact.

In 1914, Germany declared war with Russia and France. The British declared war with the Germans after their troops invaded Belgium. This ensured that German U-boats, otherwise submarines, were widely deployed for the first time. As the German army advanced in France, the first submarine patrols were also dispatched targeting British warships in the North Sea.

The first patrol had little impact, but the German U-boat U-9 was more effective. During its patrols in the North Sea, it intercepted a squadron of three British cruisers. After reloading its torpedoes, the U-boat sank all three cruisers. Alongside the U-21, it was among the first submarines to wipe out surface fleet warships.

German U-boatCredit: Image licensed under public domain on Wiki Commons.

During the war the German navy gradually expanded their U-boat missions, which primarily targeted British merchant ship supplies. However, they were not the only ships that the Germans targeted. In 1915, the Lusitania sailed towards Britain before it a German U-boat torpedoed it with thousands aboard. As the ocean liner went down within an hour, there was little time to abandon the ship.

Germany later resumed unrestricted submarine warfare in 1917. The German High Command's plan was to sever Britain's supplies by sinking a larger number of merchant ships with an expanded U – boat campaign. This campaign was initially effective, and there was a notable increase in merchant ship losses. However, as the Royal Navy provided greater convoy support for merchant ships they reduced their losses. Britain remained in the war, and the United States joined their side as U.S. naval vessels were also lost during the campaign.

After the war the German U-boat fleet was largely scrapped, as required by the Versailles Treaty. However, the world's foremost navies expanded their submarine naval fleets. The German navy also began to rebuild its U-boat fleets during the interwar period.

When Germany resumed war with Britain in 1939, U-boats were widely deployed for commerce raiding missions. Commerce raiding missions targeting merchant ship supplies were effective, but they did not have enough U-boats to win in the Atlantic. As the Allies expanded their convoy escorts, and developed more effective U-boat detection with radar and sonar, German U-boat losses increased. Allied code breakers filtered through details of approaching wolf packs so they could route their convoys round them. As such, merchant shipping losses were steadily reduced.

In the Pacific, submarine blockades were also a big part of the Allied naval tactics[1]. The Allied submarines wiped out a large proportion of Japanese merchant ship supplies during the Pacific War. Estimates suggest that 2,117 Japanese merchant ships were lost. In addition to this, Allied submarines also wiped out a number of Japanese aircraft carriers in battles such as the Battle of the Philippine Sea.

Despite the effectiveness of the Allied submarine blockade, Japan's submarines were deployed largely for surface fleet support. In battles such as the Battle of Midway the Japanese dispatched a number of submarines to intercept U.S. surface fleet ships. Only one intercepted the Yorktown aircraft carrier, after its crew had abandoned it during the battle. The aircraft carrier still remained afloat after Japanese air bombardments, but the Japanese submarine finished if off, and also wiped out the USS Hammann with its torpedoes.

The impact of the submarine in the 1940s ensured they remained a key part of NATO and Russian navies during the Cold War. The development of cruise and ballistic missiles made submarines increasingly essential during the Cold War. During the '50s the first missile-equipped submarines were constructed, such as ballistic missile subs, which supported nuclear tipped missiles. Consequently, aside from naval targets, the new generation of nuclear subs could also strike at ground targets. For the first time subs became a nuclear deterrent for the NATO and Communist navies.

As the Cold War was not strictly a war there was little in the way of direct naval combat. Cat-and-mouse naval engagements were instead the alternative. However, the USSR and USA still lost some of their submarines during the period.

Aside from the Cold War, nuclear submarines were also deployed in the Falklands. When Argentina invaded, the Royal Navy dispatched the HMS Conqueror to the Falklands. The Conqueror sank the General Belgrano. After the General Belgrano was lost, Argentina's surface fleet withdrew from the Falklands. It was the first time a nuclear submarine sank a surface fleet ship.

The Cold War submarines remain a part of the navies of today. They are versatile naval units that navies can deploy for a variety of missions. Few will doubt that submarines revolutionized naval warfare.