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