 HMS "H12" along with HMS "H11" and HMS "H13" to HMS "H20" were all built in America but were interned by the United States government until the United States entered World War I.
HMS "H12" was sold in April 1920 in Dover.Like all pre-"H21" British H-class submarines, "H12" had a displacement of at the surface and while submerged.It had a total length of , a beam length of , and a draught length of .