Unusually for the early submarine era, the E class boats displaced no more than the 340 tons of the preceding class. The E class was the first US diesel-powered submarine. The French "Z" (Q 36) was the first in the world, in 1905. Although early diesels were unreliable and the E class engines were replaced in 1915, diesels rapidly supplanted gasoline-fueled engines aboard submarines worldwide, to eliminate the substantial risk of gasoline fumes settling into the bilges of the boat at explosive concentrations. Another innovation that became standard was bow planes for greater precision in depth control.