The new design, the Mark XV, was delivered in production quality in the summer of 1931. In testing it proved to eliminate all of the problems of the earlier Mk. XI design. From altitude the prototype delivered a CEP of , while even the latest production Mk. XI's were . At higher altitudes, a series of 80 bomb runs demonstrated a CEP of . In a test on 7 October 1931, the Mk. XV dropped 50% of its bombs on a static target, the USS "Pittsburgh", while a similar aircraft with the Mk. XI had only 20% of its bombs hit.