The depth charge was invented in 1916 by British naval engineer Herbert Taylor.  His "hydrostatic pistol" could be launched out of a ship and detonated at a predetermined depth, hence the name "depth charge."  Herbert designed this weapon to combat the U-boat menace against British shipping.  The depth charge was designed to cause submarines to leak and force them to surface, where they could be shot or rammed by surface vessels.  During WWI, depth charges are credited with destroying twenty submarines.  Germany utilized 390 submarines during WWI.  

The depth charge was a defensive counter against submarines who did not have to surface in order to sink ships.  By the end of the war, Americans developed ways to launch depth charges farther from ships thus placing them closer to their targets.  Depth charge technology improved and more submarines were destroyed due to depth charges than by mines in WWII.  Submarines in WWII were also built sturdier in order to better withstand attack.