Submarine chasers flew more than 50 miles off the coast looking for enemy submarines prior to World War II.  They are attributed with reducing the massive shipping losses that occurred prior to their inception.  Some of these planes were equipped with bombs, and although very few u-boats were sunk by these airplanes, many were sunk by gunboats that were led to them by these airplanes.

NC-15345   a 24 C8C   (click on picture to see full page image)

NC-16846   a 24 C8E    (click on picture to see full page image)

NC-16812   a 24 C8F    (click on picture to see full page image)