During the war submarines also were fitted with deck guns.

Meanwhile the main operational strength of the submarine force was the boats of the and classes, 800-ton designs that resembled the German U-boats of the First World War. They proved too large to be effective coastal defense submarines and too small to be effective fleet submarines, but they played a useful role early in the Pacific War.

SONAR and ASDIC were both introduced towards the end of the war.

Fuji, Japan, was photographed through the periscope of USS  (SS-237) on war patrol, 24 May 1943.

This was done as a precaution should there be a war with Germany.

In addition to the antishipping role, Americansubmarines sometimes supported operations, particularly in the , ortransported small ,as at . During the strikes precedingthe , the experimented with deploying submarines near target to rescue downed . This proved sosuccessful (a number of aviators being rescued and the of the aviator corps beinggreatly boosted) that the deployment of lifeguard submarines became astandard feature of carrier strike planning for the remainder of thewar.

Soon discovered, the boat eventually was sold for scrap in 1868.

American submarine technology steadily improved throughout the war, with increasingly sophisticated and , more reliable , and equipment increasingly hardened against shock. Communications equipment also improved, though ironically the Allied experience with in the Atlantic meant that American submarines in the Pacific would continue limiting their communications, lest the tables be turned. However, U.S. Navy engineers had noted as early as 1918 that very low frequency radio waves could be detected at periscope depth with a suitable antenna. No use was made of this until 1941, when the of the Pacific submarine force began experimenting with underwater radio communications and suitable antennas began to be installed on submarine periscope shears. This permitted American submarines to receive instructions from ground stations even while submerged.

On 1-Feb-1917 Germany declares unrestricted submarine warfare for the third time.

merchant shipping by the end of the war

Most war-built submarines had one and sometimes two guns of about three- or four-inch caliber; however, several later German submarines carried 150-millimetre guns (including the Deutschland class in military configuration).

The submarine then visits underwater points of ..

This permitted them to approach enemy merchant ships on the surface and signal them to stop for searching (an early war policy) and later to sink small or unarmed ships that did not warrant expenditure of torpedoes.

1830Royal Bavarian Military Plenipotentiary to the War MinisterSubject: Submarine WarfareNo.

Submarine warfare is one of the four divisions of underwater ..

Even underwater, submarines are quite visible from the air, especially in shallow water or at periscope depth. They'd be quite vulnerable to overflying aircraft. Being so close to Britain, and with Allied air superiority, and in such a narrow area, they'd encounter many ASW (Anti-Submarine Warfare) aircraft, and be forced to dive limiting their speed and visibility and draining their batteries. Even underwater, they'd be vulnerable to attack from the air. Or the ASW aircraft can keep the submarine spotted and vector in surface ships.

Therefore it is necessary to attack her with every possible means ofsea and air warfare.

They had 137 submarines by the end of the war, ..

However, the U.S. Navy was poorly prepared for asubmarine war against commerce. Although a few officers had anticipatedsuch a role, in spite of the the prize rules, the submarine service hadnot for it. U.S. submarines were plagued by defective during the first two years of war, whose faults were due in part to the design emphasis on their use against heavily warships. However, once the faults were remedied,thesubmarines sank over half the ships of the Japanese merchantmarine. Losses from other causes were sufficient to practically eliminateJapanesemerchant shipping by the end of the war. American submarines alsoenjoyed significant successes against warships, accounting for six , three , a , twelve , over 40 , and numerous lesserwarships and auxiliaries. An estimated 182,000 Japanese soldiers were lost at sea from sunken transports. This was accomplished at a relatively low cost. Of the naval powers that constructed significant submarine forces, the Americans suffered the lowest casualties in the Second World War: 52 American submarines were lost, versus 74 British submarines lost, 90 Italian submarines lost, 128 Japanese submarines lost, and nearly 800 German U-boats sunk. Nevertheless, submarine service was highly dangerous. The 374 officers and 3131 men killed in American submarine operations constituted 13% of the submarine sailor corps, or over 1 in 7.

By the end of the war the depth-charge accounted for 29 kills - second only to the mine.

lay claim to the first underwater combat mission of the war

The English Channel was "covered" by the greatest concentration of Allied warships and aircraft. An all-out battle in the confines of the English Channel would not have allowed the subs sufficient (lateral) "space" or depth to operate effectively.